The influence of birth order and sibling age gap on children’s sharing decision

Abstract

The potential influences on children's sharing decision caused by birth order and sibling age gap were examined. A third-party resource allocation task was adopted to examine five- to six-year-old children's sharing decision when they expected a protagonist to allocate resources between two recipients with different social relationships. Children with sibling age gap less than three years tended to allocate resources with a closer recipient more often than those with sibling age gap more than three years. When siblings were more than three years apart in age, children allocated resources between a sibling and a friend, first-born children were more likely to choose a sibling than second-born children. However, when siblings' age gap was within three years, second-born children, in turn, were more willing to share with a sibling than first-born children. These results were attributed to the sibling relationships and the development level of the Theory of Mind.

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Early Child Development and Care
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The influence of birth order and sibling age gap on
children’s sharing decision
Erping Xiao, Hao Qin, Xinyi Zhu & Jing Jin
To cite this article: Erping Xiao, Hao Qin, Xinyi Zhu & Jing Jin (2023): The influence of birth order
and sibling age gap on children’s sharing decision, Early Child Development and Care, DOI:
10.1080/03004430.2023.2178429
To link to this article: https://doi.org/10.1080/03004430.2023.2178429
Published online: 15 Feb 2023.
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The influence of birth order and sibling age gap on children’s
sharing decision
Erping Xiao
a,b
, Hao Qin
b
, Xinyi Zhu
b
and Jing Jin
c
a
Zhejiang Philosophy and Social Science Laboratory for Research in Early Development and Childcare, Hangzhou
Normal University, Hangzhou, People’s Republic of China;
b
Jing Hengyi School of Education, Hangzhou Normal
University, Hangzhou, People’s Republic of China;
c
Foreign Languages Teaching Center, Shanghai University of
Traditional Chinese Medicine, Shanghai, People’s Republic of China
ABSTRACT
The potential influences on children’s sharing decision caused by birth
order and sibling age gap were examined. A third-party resource
allocation task was adopted to examine five- to six-year-old children’s
sharing decision when they expected a protagonist to allocate
resources between two recipients with different social relationships.
Children with sibling age gap less than three years tended to allocate
resources with a closer recipient more often than those with sibling age
gap more than three years. When siblings were more than three years
apart in age, children allocated resources between a sibling and a
friend, first-born children were more likely to choose a sibling than
second-born children. However, when siblings’age gap was within
three years, second-born children, in turn, were more willing to share
with a sibling than first-born children. These results were attributed to
the sibling relationships and the development level of the Theory of Mind.
ARTICLE HISTORY
Received 8 November 2022
Accepted 5 February 2023
KEYWORDS
Birth order; sibling age gap;
sharing decision; sibling
relationship; theory of mind
Introduction
Sharing is a prosocial skill that can facilitate people’s socialization process (Balcı, Kotaman, & Aslan,
2021). Sharing behaviour is an indispensable part of human society, which promotes sharing the
achievement from human work and the gift from nature, and develops a harmonious human
relationship. It serves as an important role in keeping a society stable. Children’s sharing behaviour
is one of the main models to present prosocial behaviour. It refers to share resource and benefit
others based on the nature of justice, equality, others’needs and the benefit of others (Ongley &
Malti, 2014). Children increase their sharing behaviour at the age between 4 and 6, especially
during the period between the age of 5 and 6 (Ugurel-Semin, 1952).
The dictator game task and the resource allocation task are common methods on children’s
sharing research. In a typical dictator game paradigm, participants are randomly paired and assigned
the role of either a dictator or a recipient. The dictator receives resources and is free to decide how
much of it is shared with an anonymous recipient. The recipient does nothing but accepts the dic-
tator’s decision (Balcıet al., 2021; Benenson, Pascoe, & Radmore, 2007; Hashimoto, Maeda, Yama-
moto, & Mifune, 2022; Kotaman & Aslan, 2021). In a typical resource allocation paradigm,
participants choose between a recipient and themselves to allocate a desirable resource (Güroğlu,
van den Bos, & Crone, 2014; House et al., 2013; Lu & Chang, 2016; Moore, 2009). The outcomes of
© 2023 Informa UK Limited, trading as Taylor & Francis Group
CONTACT Erping Xiao ep_xiao@hznu.edu.cn Zhejiang Philosophy and Social Science Laboratory for Research in Early
Development and Childcare, Hangzhou Normal University, No. 2318 Yuhangtang Rd, Yuhang District, Hangzhou, Zhejiang
Province, 311121, People’s Republic of China
Supplemental data for this article can be accessed at https://doi.org/10.1080/03004430.2023.2178429.
EARLY CHILD DEVELOPMENT AND CARE
https://doi.org/10.1080/03004430.2023.2178429

the sharing decisions have been focused on both the research on the dictator game or the resource
allocation task (Ruggeri, Luan, Keller, & Gummerum, 2018; Sabato & Eyal, 2022; Scharpf, Paulus, &
Wörle, 2017; Schäfer, Haun, & Tomasello, 2023).
To minimize participants’own motivation, a third-party resource allocation paradigm is intro-
duced to children’s sharing research. Participants are asked to help a protagonist to make a
decision on allocating resources to other characters described as siblings, friends or strangers in
a story-telling situation (Olson & Spelke, 2008; Spokes & Spelke, 2016). Research showed only chil-
drenandchildrenwithsiblingsdiffered in sharing behaviour. Childrenwithsiblingsweremore
likely than only children to expect resources to be shared with a sibling over a friend (Xiao,
Shen, & Harris, 2022).
There are many factors influencing children’s sharing decision including family education back-
ground and ways of educating children. Children with siblings showed higher prosocial behaviour
skill including sharing behaviour than only children (Stocker, Dunn, & Plomin, 1989;Xiaoetal.,
2022). Parents with a higher sense of responsibilityweremorelikelytoeducatechildrento
have more sharing behaviour (Stanhope, Bell, & Parker-Cohen, 1987). Compared with parents
with indulging, dominant, spoiling way of educating children, a democratic parenting model con-
tributed to a harmonious family atmosphere and an intimate parent–child relation (Liu & Yang,
2004).
Sibling relationship is the longest relationship lasting from birth to death (Noller, 2005). Siblings
interact when sharing knowledge, viewpoints, attitudes and feelings through physical, verbal and
nonverbal communication (Buist et al., 2016). Sibling relationship plays a pivotal role in the social
development for children and teenagers (Conger & Kramer, 2010; McHale, Updegraff, & Whiteman,
2012), especially influencing their prosocial behaviour (Buist, van Tergouw, Koot, & Branje, 2019;
Recchia & Witwit, 2017). Sibling relationships have two dimensions, positive and negative. Positive
relationship benefits a positive prediction of children’s prosocial behaviour (van der Kaap-Deeder
et al., 2015). In a positive sibling relationship, children can follow the model of siblings’moral
behaviour acquisition and internalization, which means children could imitate siblings to
produce and strengthen prosocial behaviour including sharing behaviour (Stocker et al., 1989),
while increasing negative sibling conflicts would aggravate children’s anti-social behaviour
(Dirks, Persram, Recchia, & Howe, 2015; Patterson, 1984). Children’spositive sibling relationships
increase with age (Vandell & Wilson, 1987), and enhance empathy and prosocial behaviour of chil-
dren and adolescents (Harper, Padilla-Walker, & Jensen, 2016). Conversely, negative sibling
relationships exert negative influences on children’s social development and exacerbate the risk
of their internalizing and externalizing behaviour (Buist, Deković, & Prinzie, 2013;Ruff, Durtschi,
& Day, 2018).
Birth order plays a crucial role in child development. The potential influence of birth order on the
development of social ability has historically been debated as to whether later-born siblings are to
have putative higher levels of social development (Sulloway, 2001). Later-born children with fewer
problem behaviours suggested that they may be advantaged in developing positive social behav-
iour through interactions with first-born siblings (Lawson & Mace, 2010). The first child would experi-
ence the challenge of parent–child relationship and educating model when the family relation is
restructured (Zhou & Qiao, 2014), which often induces his/her anti-social behaviour and intentions
(Chen, Wang, Liang, & Tong, 2016). Compared with the first child, the youngest child seems to
present better cooperative competence. Only when all siblings present a high level of social skill,
would the middle child have a higher level of cooperative competence than the first child (Prime,
Plamondon, & Jenkins, 2017). In addition, sex composition is also an essential characteristic of
sibling relationship, which includes female–female, male–male and female–male composition. In
general, siblings of the same sex composition, namely female–female and male–male, tend to be
more intimate (McHale et al., 2012). On the other hand, the intimate degree among siblings of
the different sex composition indicates a U-shaped development pattern (Kim, McHale, Crouter, &
Osgood, 2007).
2E. XIAO ET AL.

Age gap between siblings also influences children’s social development. Age gap is a significant
element in the cause of sibling rivalry. Greater birth spacing between siblings indicates less sibling
rivalry and higher elder sibling support due to less resource competition (Solmeyer, McHale, &
Crouter, 2014). Siblings spaced less than two years apart are more likely to possess similar abilities
than siblings spaced two to four years apart. Closer-spaced siblings are more likely to share the
same friends and peers than those spaced further apart. Wider age spacing is associated with less
conflict between siblings (Kolak & Volling, 2013). A smaller age gap leads to more conflicts, compa-
nied by a higher level of the co-existence of intimacy and conflicts (Buist & Vermande, 2014).
However, a big age gap does not benefit individual development as well (Riordan, Morris, Hattie,
& Stark, 2012). An ideal age gap is suggested to be three years between siblings (Campione-Barr,
2017; Cornoldi & Fattori, 1976).
Social cognition theory believes cognitive development is an important mechanism in promoting
sharing behaviour, which includes theory of mind and empathy (Smith, Blake, & Harris, 2013). Theory
of mind is a social cognition skill which can influence children’s sharing behaviour positively and children
with a stronger social cognition skill are more likely to enjoy sharing with others (Rochat et al., 2009).
Research suggests that the first-born child in a family plays a positive role in promoting the second-
born child’s psychological development (Ruffman, Slade, & Crowe, 2002), which could be attributed
to the secondchild often learns more advanced language from the older one and thereby improves cog-
nitive development through sibling interaction (McAlister & Peterson, 2013). There is no consensus
whether the same impact the second child plays on the first child. On the one hand, some research
claims that the second child hinders the first child’s psychological development because the old child
often experiences a decreased sense of security, the occurrence of anxiety and resistance with the
arrival of the later-born child (Gullicks & Crase, 1993;Wright&Mahfoud,2012). On the other hand,
the older child often develops his/her psychological development in the process of passing knowledge
to the younger sibling (Davis-Unger & Carlson, 2008). Similarly, an age gap which is either too big ortoo
small also does not benefit psychological development. A child with a sibling who is 12 years younger or
older, does seem to be significantly improved his/her psychological level compared with the only child
(Peterson, 2000). Empathy is the motivation foundation of sharing behaviour (Hoffman, 1981). Research
indicates that a six-year-old first child tends to have a higher level of transference than a five-year-old
counterpart; similarly, a child with a four-year gap sibling also shows a significant lower level of transfer-
ence than a child with a three-year gap sibling (Zhang, Cai, Ran, & Xia, 2019).
Changes of the national population policy in China have impacted on family structure. It has been
more than 40 years since the one-child-per-couple policy was implemented in 1979. Since 2009,
parents have been allowed to give birth to two children if they are both only children themselves,
and since 2014 if one of them is an only child (Basten & Jiang, 2014; Ouyang, 2013). Since 2016, the
population policy in China has undergone an important reform, that is, a universal two-child policy
has replaced the previous one-child policy (Padmadas, 2017). In 2021, the Chinese government has
further optimized the national population policy, which allowed a couple to have three children.
These changes have led to the current structure of Chinese families dominated by one-child families
and two-child families, especially in families with young children (Xiao et al., 2022).
The current study focuses on children aged five to six years old when sharing behaviour is in a
significant development. Baby boomers born after the implementation of the universal two-child
policy in 2016 are now five to six years old. Due to the unique population policy, the family structure
is transferring from the only-child family to multi-child family, and there are two siblings in most of
the multi-child families. Changes in family structure have simultaneously brought new challenges to
sibling relations. As mentioned earlier, sibling relations influence children’s prosocial behaviour in a
complex way. It follows the question whether birth order and sibling age gap also influence-sharing
decision, which is the purpose of the current study. A third-party resource allocation task was
adopted to explore individual differences of sharing decision among children in their allocation of
resources between two recipients, e.g. a sibling vs. a stranger, a friend vs. a stranger and a sibling
vs. a friend (Olson & Spelke, 2008; Spokes & Spelke, 2016; Xiao et al., 2022).
EARLY CHILD DEVELOPMENT AND CARE 3

Method
Participants
One hundred twenty children between five and six years old were invited to participate in the study.
All participants were recruited through public kindergartens in Hangzhou City, Zhejiang Province in
China. The public kindergartens are funded by the government and serve children aged three to six
years old who live nearby. The preschool education in China is not mandatory but the gross enrol-
ment rate for preschool children reached 88.1% nationwide, which is 99.15% in Hangzhou City. The
average teacher–student ratio is 1:10 and all teachers in Hangzhou public kindergartens have college
degrees or above. Participants were all from two-child families and were divided into four groups
according to their sibling age gap and birth order. Each group consisted of 30 children. The infor-
mation of the participants is shown in Table 1.
The study was approved by the Scientific Research Ethics Committee of Hangzhou Normal Uni-
versity. Parents or legal guardians of the minors were informed of the nature and content of the
study, and gave either oral or written consent to allow their minor children to participate, and all
the minors also gave their oral assent prior to participating in this study. All participants received
a gift for completing the study.
Procedure
First of all, the conceptual understanding of siblings and friends from preschoolers was evaluated.
The youngsters were then given a resource allocation assignment to complete an interactive
story-telling session. While choosing between a selected set of receivers, the story protagonist
would divide a given resource to one of them. Next, children were requested to anticipate who
would be given the resources in the resource allocation task (i.e. a sibling vs. a stranger; a friend
vs. a stranger; and a sibling vs. a friend). The current study’s materials and techniques are consistent
with those in the previous research (Xiao et al., 2022), and belong to the same series of studies.
The introductory phase
The aim of the introductory phase was to ensure that the participants understood the procedure of
resource allocation task. The participant was introduced a story about a boy with two pets, a dog and
a cat. The participant was then informed that there was a bell possessed by the boy, which attracted
both the dog and the cat. The task was to assist the boy in deciding which pet could get the bell. The
child was also encouraged to follow his/her ideas, placing the bell picture in front of the picture of
the pet. If a child expressed a desire to offer a bell to both pets, he/she was reminded that he/she
only had one choice because only one bell could be given.
The sharing phase
Participants were initially exposed to a scene including characters and the only resource. All charac-
ters, (i.e. a protagonist, a sibling, a friend, a stranger) and their relationships were introduced before
the storyline. The protagonist and the sibling were described as having the same mother; the pro-
tagonist and the friend always played together and shared the same class in kindergarten; the
Table 1. The general information of the participants.
Birth order Sibling age gap Boys (N, %) Age (M±SD)
a
First born More than three years 14, 47% 68.80 ± 0.57
Less than three years 17, 57% 69.32 ± 0.88
Second born More than three years 20, 67% 69.11 ± 1.01
Less than three years 12, 40% 69.17 ± 0.56
a
Age is measured in months.
4E. XIAO ET AL.

protagonist and the stranger never met before. All the characters had the same age and gender as
the participant.
The second step was asking a series of paired control questions before the allocation task to
ensure that the participants understood the relationships between the protagonist and each char-
acter. If children gave the wrong answer to any of the questions, they would be told the right
answer. Also, they would be offered another set of comparable questions. If children answered
the question incorrectly again, they were excluded from the following task.
The paired questions for sibling and friend were: ‘Who has the same parents as Lulu (the prota-
gonist)?’and ‘Who did Lulu first meet at the kindergarten?’The paired questions for friend and stran-
ger were: ‘Who has Lulu played with many times before?’and ‘Who has Lulu not met before?’The
paired questions for sibling and stranger were: ‘Who does Lulu live with in the same house?’and
‘Who does Lulu not know much about?’
Children were giving one of three separate situations featuring the protagonist and a pair of char-
acters, sibling and friend, sibling and stranger, or friend and stranger. These control questions were
followed by these scenarios. The specifics of the plot and the background image of a park were the
same, but the images of the characters changed depending on various events. The three pairs were
arranged in a counterbalanced order among all participants. The following is an example of the
Resource Allocation Task script:
It was a sunny Sunday. Lulu went to the park. She met her friend and a girl she had never seen before there. They
all played together. Lulu brought one delicious cupcake. Who do you think Lulu would share the ONLY cupcake
with?
The participants were then asked to think about whom the protagonist would like to offer the
cupcake to. The picture of the cupcake was to be placed next to the picture of the character the pro-
tagonist was supposed to offer the cupcake. Finally, participants were inquired about their choices
and why.
Results
Children’s choices of sharing decision were recorded as raw data (see Table 2). To further explore the
differences caused by birth order and sibling age gap, a binomial distribution was analysed children’s
expectations on resource allocation. The raw data were coded as follows. Children’s responses were
scored as a 1 if they choose to share with the closer character, e.g. sibling in sibling vs. friend, friend
in friend vs. stranger and sibling in sibling vs. stranger. The opposite responses were coded as a 0
instead (Xiao et al., 2022).
Children’s sharing responses for each recipient pair using the above scoring rules were analysed.
A 2 (birth order: first born vs. second born) by 2 (age gap: more than three years old vs. less than
three years old) by 3 (recipient pair: sibling–friend vs. sibling–stranger vs. friend–stranger) mixed-
model, multivariate analysis of variance (MANOVA) was conducted (see Table 3).
The results revealed a main effect of age gap, F(1,116) = 6.64, p< .05, η
2
= 0.05. The interaction had
significant effects between age gap and birth order, F(1,116) = 1.88, p< .01, η
2
= 0.06, and between
age gap and recipient pair, F(2,232) = 3.22, p< .05, η
2
= 0.03, and among age gap, birth order, and
Table 2. Children’s responses of sharing decision by birth order, sibling age gap and recipient pair.
Birth order Sibling age gap
Sibling vs. friend Sibling vs. stranger Friend vs. stranger
Sibling Friend Sibling Stranger Friend Stranger
First born More than three years 28 2 21 9 19 11
Less than three years 18 12 23 7 26 4
Second born More than three years 16 14 22 8 15 15
Less than three years 27 3 27 3 24 6
The numbers in the table are the number of choices.
EARLY CHILD DEVELOPMENT AND CARE 5

recipient pair, F(2,232) = 6.45, p< .01, η
2
= 0.05. Regarding the age gap effect, children whose sibling’s
age gap with less than three years old (M= 0.67, SE = 0.04) were generally more willing than those
whose sibling’s age gap with more than three years old (M= 0.81, SE = 0.04, p= .01) to allocate
resources to the closer character. Regarding the age gap and birth order interaction effect, among
children whose sibling’s age gap with more than three years old, first-born children (M= 0.76, SE =
0.05) favoured the closer character more than second-born children (M= 0.59, SE = 0.05, p= .03).
Among second-born children, children whose sibling’s age gap with less than three years old (M=
0.87, SE = 0.05) were more willing to allocate resources to the closer character than those whose sib-
ling’s age gap with more than three years old (M= 0.59, SE = 0.05, p< .001) (see Figure 1).
According to the age gap and recipient pair interaction effect, among children whose sibling’s
age gap with more than three years old, they were more systematic in choosing a sibling over a
friend (M= 0.73, SE = 0.05) or a stranger (M= 0.72, SE = 0.04) than a friend over a stranger (M=
0.57, SE = 0.06, p= 0.04), but no significant difference was observed between sibling–friend and
sibling–stranger pairs (p= .41). In the case of allocating resources to a friend and a stranger, children
whose sibling’s age gap with less than three years old (M= 0.83, SE = 0.06) favoured the closer
character more than those whose sibling’s age gap with more than three years old (M= 0.57, SE =
0.06, p=.001) (see Figure 2).
According to age gap, birth order and recipient pair three-factor interaction effect, in the case of
allocating resources to a sibling and a friend, among children whose sibling’s age gap with more
than three years old, first-born children (M= 0.93, SE = 0.07) favoured a sibling over a friend more
than second-born children (M= 0.53, SE = 0.07, p< .001), while among those whose sibling’s age
gap with less than three years old, the case of sharing was just the opposite. That is, first-born chil-
dren (M= 0.60, SE = 0.07) favoured a sibling over a friend less than second-born children (M= 0.90,
SE = 0.07, p= .005). In the case of allocating resources between a sibling and a friend, first-born chil-
dren whose sibling’s age gap with more than three years old (M= 0.93, SE = 0.07) favoured a sibling
over a friend more than those whose sibling’s age gap with less than three years old (M= 0.60, SE =
0.07, p= .002), while in the case of allocating resources between a friend and a stranger, the case of
sharing was just the opposite. That is, first-born children whose sibling’s age gap with more than
three years old (M= 0.63, SE = 0.08) favoured a friend over a stranger less than those whose sibling’s
age gap with less than three years old (M= 0.87, SE = 0.08, p= .04).
Children with different birth orders and sibling age gap showed different patterns when engaging
in sharing decision. For children with sibling age gap more than three years old, first-born children
chose a sibling over a friend more than a sibling over a stranger more than a friend over a stranger,
while second-born children chose a sibling over a stranger more than a sibling over a friend more than
a friend over a stranger. For children with sibling age gap less than three years old, first-born children
embodied the exact opposite order of preference to children with sibling age gap more than three
years old. Specifically, children whose sibling age gap with less than three years old favoured a
friend over a stranger more than a sibling over a stranger more than a sibling over a friend.
Discussion
This study aimed to compare the effects of birth order and sibling age differences on sharing
decision in children aged from five to six years old. The results showed that birth or-der and
Table 3. Mean proportion of sharing with closer recipient by birth order, sibling age gap and recipient pair (M±SD).
Recipient pair
First born Second born
More than three years Less than three years More than three years Less than three years
Sibling vs. friend 0.93 ± 0.25 0.60 ± 0.50 0.53 ± 0.51 0.90 ± 0.31
Sibling vs. stranger 0.70 ± 0.47 0.77 ± 0.43 0.73 ± 0.45 0.90 ± 0.31
Friend vs. stranger 0.63 ± 0.49 0.87 ± 0.35 0.50 ± 0.51 0.80 ± 0.41
6E. XIAO ET AL.

sibling age gap had an effect on sharing decision, with first-born children with a sibling age gap of
three years or more preferring to share with their siblings than first-born children with an age gap of
less than three years. Conversely, second-born children with an age gap of less than three years pre-
ferred to share with their siblings compared to second-born children with a sibling age gap of three
years or more. Previous studies have shown that kin-ship preferences emerge at age 5 and develop
Figure 1. Mean proportion of sharing with closer recipient by age gap and birth order. The scores range from 0 to 1. Error bars
indicate standard errors of the means. The same below.
Figure 2. Mean proportion of sharing with closer recipient by age gap and recipient pair.
EARLY CHILD DEVELOPMENT AND CARE 7

steadily at age 6 (Lu & Chang, 2016; Spokes & Spelke, 2016). The present study draws more
detailed conclusions than the above findings. Next, we considered two possible explanations for
this result: the effects of the sibling relationships and the level of development of children’s
theory of mind.
Sibling relationships
In general, the sibling relationships influences young children’s sharing decision. In previous studies,
children with siblings did not show a significant preference for siblings over best friends, and chil-
dren’s choices were influenced by sibling conflict. Sibling conflict is a competition for parental invest-
ment or other survival benefits, and ‘sibling rivalry’is typical in animal and human societies (Coe,
Palmer, Palmer, & DeVito, 2010). Preferences for resource allocation in sibling vs. best friend
groups are also greatly influenced by sibling conflict, with vicious sibling rivalry leading to
reduced preferences for sibling kin selection in children (Spokes & Spelke, 2016).
In the present study, the sibling age gap was a significant independent variable influencing chil-
dren’s sharing decision. The age difference between siblings is a unique family ecology. A smaller
age difference is one of the influencing factors that trigger sibling conflict. The smaller the age differ-
ence, the more external behavioural problems are induced (Buist et al., 2013). Such conflicting
behaviour is more evident when all siblings are in the preschool stage (Lamb, 1978).
The effect of sibling age gap diminishes as the child ages. The quality of sibling relationships
usually progresses in the direction of positive affect as children age (Vandell & Wilson, 1987).
From this perspective, the first-born preschoolers whose siblings have an age gap of more than
three years in the present study were accompanied by a younger sibling who had just been born
or had not yet entered kindergarten. There were few common topics and few opportunities for com-
munication among siblings due to the large age gap. At the same time, to a certain extent, sibling
conflicts are avoided, so the sibling relationships are relatively harmonious. As first-born children get
older, they become less impulsive and have more control over their behaviour, and thus reducing
sibling conflicts and being more willing to share with their siblings. In contrast, the first-born pre-
schoolers whose siblings have an age gap of less than three years in the present study were
accompanied by a sibling who was also in kindergarten. Siblings share more psychological and
behavioural similarities. Thus, the in-crease of sibling interaction brings about the increase of contra-
dictions and conflicts. Most preschool siblings have a strong emotional relationship, in which the
high-level conflict and high-level harmony coexist. It will bring significant uncertainty to children’s
sharing behaviour (Buist & Vermande, 2014). It is important to note that, when the sibling age
gap is within three years, namely siblings are similar in age, the age effect (i.e. the older sibling
prefers to share with the younger sibling) disappears, or even shows the opposite behaviour
trend. First-born children choose to favour a friend over a stranger more than a sibling over a stran-
ger when allocating resources. When siblings are similar in age, there is more commonality in how
siblings get along with each other, and at the same time, there is a greater chance of conflict. As the
Chinese proverb says, distance creates beauty. At this point, children are more inclined to share with
the less close recipient.
As stated in Introduction, most of the second children born after the universal two-child policy
are now at the age of five to six years old, which happens to be the target population of the
current study. Most of their older brothers or sisters are already in secondary school or even
college. In this particular case, the excessive sibling age gap makes sibling relationships somewhat
distant. The sibling relationship with a sibling age difference of more than three years is not par-
ticularly close, but conflict behaviours are rare. Second-born children get help from their older sib-
lings in daily life, increasing their admiration and affection for their older siblings. On the other
hand, first-born children may feel protective of their younger siblings because of their young
age. Thus, children with a sibling age gap above three years show more kin preference in
sharing decision.
8E. XIAO ET AL.

Theory of mind
Theory of Mind (ToM) refers to the ability of understanding that individuals are mental beings,
with thoughts, feelings and intentions that explain their behaviour (Chilton, Mayer, & McCracken,
2019; Hughes & Devine, 2019). It describes the ability to engage in perspective-taking, infer
mental states, and predict intentions, behaviour and actions in others (Spokes & Spelke, 2016).
As an essential social competence, the theory of mind influences children’s early prosocial behav-
iour. Four to seven years old is the turning point and maturity period of children’s theory of
mind. As children become more sensitive to and master others’mental states, they can infer
others’needs and emotions and thus are more inclined to share equally (Takagishi, Kameshima,
Schug, Koizumi, & Yamagishi, 2010). The influence of family microsystems on children’s theory of
mind includes parent–child interaction, sibling interaction, basic family environment and sibling
relationship structure (Shang & Mo, 2010). Sibling relationship structure includes aspects such
as the number of siblings, gender structure, birth order and sibling age gap. Previous studies
have shown that preschoolers with one or more siblings have better development levels of
theory of mind than only children (Perner, Ruffman, & Leekam, 1994; Vonk, Jett, Tomeny,
Mercer, & Cwikla, 2020). The birth of a second child facilitates, to some extent, the theory of
mind development of the older child (Paine, Pearce, van Goozen, de Sonneville, & Hay, 2018),
or the older child acts as a mentor to help the second child acquire theory of mind earlier (Far-
hadian, Gazanizad, & Shakerian, 2011; Kennedy, Lagattuta, & Sayfan, 2015;Ruffman, Perner, Naito,
Parkin, & Clements, 1998). Preschoolers’interaction with their siblings maximizes the develop-
ment of children’s theory of mind. The similarity in the age of preschoolers’siblings facilitates
the development of children’s theory of mind levels more than their infant or adolescent siblings
(Peterson, 2000).
Recent research suggests that young children’s theory of mind predicts more sharing behaviours
(Brock, Kim, Gutshall, & Grissmer, 2019). In the present study, the participants were preschoolers,
both first-born and second-born children, and with a sibling age gap of fewer than three years
may generate more sibling conflict and acquire better levels of theory of mind development
during more sibling interactions than children with a tremendous age difference due to the more
competitive nature of limited family resources. Thus, children with greater sibling age gap are
more inclined to engage in generous sharing decisions.
There are a few limitations in the current study. Firstly, children’s birth order and sibling age
gap were the key variables in the current study. Other variables, such as the gender structure of
siblings, the quantity and quality of the sibling relationships, might also potentially influence
children’s sharing decision. Future research could explore above factors more in-depth.
Secondly, future research could explore whether Theory of Mind influences children’ssharing
decision directly. Also, it would have been better to control parental attitudes and practices
on children’s sharing decision. Future studies could compare the potential impact of different
parenting.
Conclusion
Overall, children whose siblings were less than three years apart tended to share re-source items with
a close party more often than children who were more than three years apart. When siblings were
more than three years apart in age, children were more likely to share resources with siblings
(siblings vs. friends or strangers) and less likely to share re-sources with friends (friends vs. strangers).
When children shared resources with siblings and friends, first-born children were more likely to
share resources with a close party than second-born children. When children with a sibling age
gap of three years or less shared resources with siblings and friends, second-born children were
more willing to share with siblings than first-born children. Age gap and birth order together
influenced children’s sharing decision.
EARLY CHILD DEVELOPMENT AND CARE 9

Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This work was supported by the Key Cultivation Project in the College of Education of Hangzhou Normal University
under grant number 20JYXK013; and Foundation Project of China Youth and Children Research Association under
grant number 2022B20.
Notes on contributors
Erping Xiao is an associate professor in Jing Hengyi School of Education at Hangzhou Normal University. Her research is
focused on children’s cognition, developmental psychology and cross–cultural psychology. Her professional back-
ground is psychology.
Hao Qin is a graduate student in Jing Hengyi School of Education at Hangzhou Normal University.
Xinyi Zhu is a graduate student in Jing Hengyi School of Education at Hangzhou Normal University.
Jing Jin is a lecturer in Foreign Languages Teaching Center at Shanghai University of Traditional Chinese Medicine. Her
research is focused on language development and cultural studies.
ORCID
Erping Xiao http://orcid.org/0000-0002-7096-5460
References
Balcı, A., Kotaman, H., & Aslan, M. (2021). Impact of earning on young children’s sharing behaviour. Early Child
Development and Care,191(11), 1757–1764. doi:10.1080/03004430.2019.1674294
Basten, S., & Jiang, Q. (2014). China’s family planning policies: Recent reforms and future prospects. Studies in Family
Planning,45(4), 493–509. doi:10.1111/j.1728-4465.2014.00003.x
Benenson, F. J., Pascoe, J., & Radmore, N. (2007). Children’s altruistic behavior in the dictator game. Evolution and Human
Behavior,28, 168–175. doi:10.1016/j.evolhumbehav.2006.10.003
Brock, L. L., Kim, H., Gutshall, C. C., & Grissmer, D. W. (2019). The development of theory of mind: Predictors and mod-
erators of improvement in kindergarten. Early Child Development and Care,189(12), 1914–1924. doi:10.1080/
03004430.2017.1423481
Buist, K. L., Deković, M., & Prinzie, P. (2013). Sibling relationship quality and psychopathology of children and adoles-
cents: A meta-analysis. Clinical Psychology Review,33(1), 97–106. doi:10.1016/j.cpr.2012.10.007
Buist, K. L., van Tergouw, M. S., Koot, H. M., & Branje, S. (2019). Longitudinal linkages between older and younger sibling
depressive symptoms and perceived sibling relationship quality. Journal of Youth and Adolescence,48(6), 1190–1202.
doi:10.1007/s10964-019-01009-y
Buist, K. L., Verhoeven, M., Hoksbergen, R., ter Laak, J., Watve, S., & Paranjpe, A. (2016). Associations of perceived sibling
and parent-child relationship quality with internalizing and externalizing problems: Comparing Indian and Dutch
early adolescents. The Journal of Early Adolescence,37(8), 1163–1190. doi:10.1177/0272431616653473
Buist, K. L., & Vermande, M. (2014). Sibling relationship patterns and their associations with child competence and
problem behavior. Journal of Family Psychology,28(4), 529–537. doi:10.1037/a0036990
Campione-Barr, N. (2017). The changing nature of power, control, and influence in sibling relationships. New Directions
for Child and Adolescent Development,2017(156), 7–14. doi:10.1002/cad.20202
Chen, B., Wang, Y., Liang, J., & Tong, L. (2016). And baby makes four: Biological and psychological changes and influen-
tial factors of firstborn’s adjustment to transition to siblinghood. Advances in Psychological Science,24(6), 863–873.
doi:10.3724/sp.j.1042.2016.00863
Chilton, H., Mayer, C., & McCracken, W. (2019). Evidence of theory of mind in the written language of deaf children. The
Journal of Deaf Studies and Deaf Education,24(1), 32–40. doi:10.1093/deafed/eny027
Coe, M. K., Palmer, A. L., Palmer, C. T., & DeVito, C. L. (2010). Culture, altruism, and conflict between ancestors and des-
cendants. Structure and Dynamics: EJournal of Anthropological and Related Sciences,4, 3. doi:10.5070/sd943003314
Conger, K. J., & Kramer, L. (2010). Introduction to the special section: Perspectives on sibling relationships: Advancing
child development research. Child Development Perspectives,4(2), 69–71. doi:10.1111/j.1750-8606.2010.00120.x
10 E. XIAO ET AL.

Cornoldi, C., & Fattori, L. C. (1976). Age spacing in firstborns and symbiotic dependence. Journal of Personality and Social
Psychology,33(4), 431–434. doi:10.1037/0022-3514.33.4.431
Davis-Unger, A. C., & Carlson, S. M. (2008). Development of teaching skills and relations to theory of mind in preschoo-
lers. Journal of Cognition and Development,9(1), 26–45. doi:10.1080/15248370701836584
Dirks, M. A., Persram, R., Recchia, H. E., & Howe, N. (2015). Sibling relationships as sources of risk and resilience in the
development and maintenance of internalizing and externalizing problems during childhood and adolescence.
Clin Psychology Review,42, 145–155. doi:10.1016/j.cpr.2015.07.003
Farhadian, M., Gazanizad, N., & Shakerian, A. (2011). Theory of mind and siblings among preschool children. Asian Social
Science,7, 3. doi:10.5539/ass.v7n3p224
Gullicks, J. N., & Crase, S. J. (1993). Sibling behavior with a new born: Parents’expectations and observations. Journal of
Obstetric, Gynecologic & Neonatal Nursing,22(5), 438–444. doi:10.1111/j.1552-6909.1993.tb01827.x
Güroğlu, B., van den Bos, W., & Crone, E. A. (2014). Sharing and giving across adolescence: An experimental study exam-
ining the development of prosocial behavior. Frontiers in Psychology,5,1–13. doi:10.3389/fpsyg.2014.00291
Harper, J. M., Padilla-Walker, L. M., & Jensen, A. C. (2016). Do siblings matter independent of both parents and friends?
Sympathy as a mediator between sibling relationship quality and adolescent outcomes. Journal of Research on
Adolescence,26(1), 101–114. doi:10.1111/jora.12174
Hashimoto, H., Maeda, K., Yamamoto, K., & Mifune, N. (2022). Willingness to be the recipient during the dictator game.
BMC Research Notes,15(1), 261. doi:10.1186/s13104-022-06148-3
Hoffman, M. L. (1981). Is altruism part of human nature? Journal of Personality and Social Psychology,40(1), 121–137.
doi:10.1037/0022-3514.40.1.121
House, B. R., Silk, J. B., Henrich, J., Barrett, H. C., Scelza, B. A., Boyette, A. H., & Laurence, S. (2013). Ontogeny of prosocial
behavior across diverse societies. Proceedings of the National Academy of Sciences of the United States of America,110
(36), 14586–14591. doi:10.1073/pnas.1221217110
Hughes, C., & Devine, R. T. (2019). Learning to read minds: A synthesis of social and cognitive perspectives. In D.
Whitebread, et al. (Eds.), The sage handbook of developmental psychology and early childhood education (1st ed.,
pp. 118-169). Los Angeles: SAGE Publications Ltd. doi:10.4135/9781526470393
Kennedy, K., Lagattuta, K. H., & Sayfan, L. (2015). Sibling composition, executive function, and children’s thinking about
mental diversity. Journal of Experimental Child Psychology,132, 121–139. doi:10.1016/j.jecp.2014.11.007
Kim, J.-Y., McHale, S. M., Crouter, A. C., & Osgood, D. W. (2007). Longitudinal linkages between sibling relationships and
adjustment from middle childhood through adolescence. Developmental Psychology,43(4), 960–973. doi:10.1037/
0012-1649.43.4.960
Kolak, A. M., & Volling, B. L. (2013). Coparenting moderates the association between firstborn children’s temperament
and problem behavior across the transition to siblinghood. Journal of Family Psychology,27(3), 355–364. doi:10.1037/
a0032864
Kotaman, H., & Aslan, M. (2021). Whom to share teacher, joker or stranger. International Journal of Early Years Education.
doi:10.1080/09669760.2021.1971515
Lamb, M. E. (1978). Interactions between eighteen-month-olds and their preschool-aged siblings. Child Development,49
(1), 51. doi:10.2307/1128592
Lawson, D. W., & Mace, R. (2010). Siblings and childhood mental health: Evidence for a later-born advantage. Social
Science & Medicine,70(12), 2061–2069. doi:10.1016/j.socscimed.2010.03.009
Liu, W., & Yang, L. (2004). Study on the relations among children’s social inhibition, parenting and altruism. Psychological
Development and Education,1,6–11.
Lu, H. J., & Chang, L. (2016). Resource allocation to kin, friends, and strangers by 3- to 6-year-old children. Journal of
Experimental Child Psychology,150, 194–206. doi:10.1016/j.jecp.2016.05.018
McAlister, A. R., & Peterson, C. C. (2013). Siblings, theory of mind, and executive functioning in children aged 3-6 years:
New longitudinal evidence. Child Development,84(4), 1442–1458. doi:10.1111/cdev.12043
McHale, S. M., Updegraff, K. A., & Whiteman, S. D. (2012). Sibling relationships and influences in childhood and adoles-
cence. Journal of Marriage and Family,74(5), 913–930. doi:10.1111/j.1741-3737.2012.01011.x
Moore, C. (2009). Fairness in children’s resource allocation depends on the recipient. Psychological Science,20(8), 944–
948. doi:10.1111/j.1467-9280.2009.02378.x
Noller, P. (2005). Sibling relationships in adolescence: Learning and growing together. Personal Relationships,12(02), 1–
22. doi:10.1111/j.1350-4126.2005.00099.x
Olson, K. R., & Spelke, E. S. (2008). Foundations of cooperation in young children. Cognition,108(1), 222–231. doi:10.
1016/j.cognition.2007.12.003
Ongley, S. F., & Malti, T. (2014). The role of moral emotions in the development of children’s sharing behavior.
Developmental Psychology,50(4), 1148–1159. doi:10.1037/a0035191
Ouyang, Y. (2013). China relaxes its one-child policy. The Lancet,382(9907), e28, doi:10.1016/s0140-6736(13)62544-1
Padmadas, S. S. (2017). Two-child policy in China: Rhetoric versus reality. Annals of Human Biology,44(2), 97–98. doi:10.
1080/03014460.2016.1177113
EARLY CHILD DEVELOPMENT AND CARE 11

Paine, A. L., Pearce, H., van Goozen, S. H. M., de Sonneville, L. M. J., & Hay, D. F. (2018). Late, but not early, arriving
younger siblings foster firstborns’understanding of second-order false belief. Journal of Experimental Child
Psychology,166, 251–265. doi:10.1016/j.jecp.2017.08.007
Patterson, G. (1984). Siblings: Fellow travelers in coercive family processes. Advances in the Study of Aggression, 173–215.
doi:10.1016/b978-0-12-037701-5.50010-6
Perner, J., Ruffman, T., & Leekam, S. R. (1994). Theory of mind is contagious: You catch it from your sibs. Child
Development,65(4), 1228. doi:10.2307/1131316
Peterson, C. C. (2000). Kindred spirits: Influences of siblings’perspectives on theory of mind. Cognitive Development,15
(4), 435–455. doi:10.1016/s0885-2014(01)00040-5
Prime, H., Plamondon, A., & Jenkins, J. M. (2017). Birth order and preschool children’s cooperative abilities: A within-
family analysis. British Journal of Developmental Psychology,35(3), 392–405. doi:10.1111/bjdp.12180
Recchia, H. E., & Witwit, M.-a. (2017). Family perspectives on siblings’conflict goals in middle childhood: Links to hier-
archical and affective features of sibling relationships. New Directions for Child and Adolescent Development,2017
(156), 33–48. doi:10.1002/cad.20198
Riordan, D. V., Morris, C., Hattie, J., & Stark, C. (2012). Interbirth spacing and offspring mental health outcomes.
Psychological Medicine,42(12), 2511–2521. doi:10.1017/s0033291712000888
Rochat, P., Dias, M. D., Guo, L., Broesch, T., Passos-Ferreira, C., Winning, A., & Berg, B. (2009). Fairness in distributive justice
by 3- and 5-year-olds across seven cultures. Journal of Cross-Cultural Psychology,40(3), 416–442. doi:10.1177/
0022022109332844
Ruff,S. C., Durtschi, J. A., & Day, R. D. (2018). Family subsystems predicting adolescents’perceptions of sibling relation-
ship quality over time. Journal of Marital and Family Therapy,44(3), 527–542. doi:10.1111/jmft.12265
Ruffman, T., Perner, J., Naito, M., Parkin, L., & Clements, W. A. (1998). Older (but not younger) siblings facilitate false belief
understanding. Developmental Psychology,34(1), 161–174. doi:10.1037/0012-1649.34.1.161
Ruffman, T., Slade, L., & Crowe, E. (2002). The relation between children’s and mothers’mental state language and
theory-of-mind understanding. Child Development,73(3), 734–751. doi:10.1111/1467-8624.00435
Ruggeri, A., Luan, S., Keller, M., & Gummerum, M. (2018). The influence of adult and peer role models on children’and
adolescents’sharing decisions. Child Development,89(5), 1589–1598. doi:10.1111/cdev.12916
Sabato, H., & Eyal, T. (2022). Proud to help when i should: Children’s positive emotions following sharing decisions with a
needy versus not-needy other. Journal of Experimental Child Psychology,219, 105400. doi:10.1016/j.jecp.2022.105400
Scharpf, F., Paulus, M., & Wörle, M. (2017). The impact of social relationships on Ugandan children’s sharing decisions.
European Journal of Developmental Psychology,14(4), 436–448. doi:10.1080/17405629.2016.1231062
Schäfer, M., Haun, D. B. M., & Tomasello, M. (2023). Children’s consideration of collaboration and merit when making
sharing decisions in private. Journal of Experimental Child Psychology,228, 105609. doi:10.1016/j.jecp.2022.105609
Shang, C., & Mo, S. (2010). The influence of family microsystems on children’s theory of mind: Factors. Process and mech-
anism. Advances in Psychological Science,6, 914–923. https://journal.psych.ac.cn/xlkxjz/CN/Y2010/V18/I6/914
Smith, C. E., Blake, P. R., & Harris, P. L. (2013). I should but I won’t: Why young children endorse norms of fair sharing but
do not follow them. PLoS ONE,8, 3. doi:10.1371/journal.pone.0059510
Solmeyer, A. R., McHale, S. M., & Crouter, A. C. (2014). Longitudinal associations between sibling relationship qualities
and risky behavior across adolescence. Developmental Psychology,50(2), 600–610. doi:10.1037/a0033207
Spokes, A. C., & Spelke, E. S. (2016). Children’s expectations and understanding of kinship as a social category. Frontiers in
Psychology,7. doi:10.3389/fpsyg.2016.00440
Stanhope, L., Bell, R. Q., & Parker-Cohen, N. Y. (1987). Temperament and helping behavior in preschool children.
Developmental Psychology,23(3), 347–353. doi:10.1037/0012-1649.23.3.347
Stocker, C., Dunn, J., & Plomin, R. (1989). Sibling relationships: Links with child temperament, maternal behavior, and
family structure. Child Development,60(3), 715. doi:10.2307/1130737
Sulloway, F. J. (2001). Birth order, sibling competition, and human behavior. In H. R. Holcomb (Ed.), Conceptual chal-
lenges in evolutionary psychology (pp. 39–83). Dordrecht: Springer.
Takagishi, H., Kameshima, S., Schug, J., Koizumi, M., & Yamagishi, T. (2010). Theory of mind enhances preference for fair-
ness. Journal of Experimental Child Psychology,105(1-2), 130–137. doi:10.1016/j.jecp.2009.09.005
Ugurel-Semin, R. (1952). Moral behavior and moral judgment of children. The Journal of Abnormal and Social Psychology,
47(2, Suppl), 463–474. doi:10.1037/h0056970
van der Kaap-Deeder, J., Vansteenkiste, M., Soenens, B., Loeys, T., Mabbe, E., & Gargurevich, R. (2015). Autonomy-sup-
portive parenting and autonomy-supportive sibling interactions. Personality and Social Psychology Bulletin,41(11),
1590–1604. doi:10.1177/0146167215602225
Vandell, D. L., & Wilson, K. S. (1987). Infants’interactions with mother, sibling, and peer: Contrasts and relations between
interaction systems. Child Development,58(1), 176. doi:10.2307/1130299
Vonk, J., Jett, S. E., Tomeny, T. S., Mercer, S. H., & Cwikla, J. (2020). Young children’s theory of mind predicts more sharing
with friends over time. Child Development,91(1), 63–77. doi:10.1111/cdev.13112
Wright, B., & Mahfoud, J. (2012). A child-centred exploration of the relevance of family and friends to theory of mind
development. Scandinavian Journal of Psychology,53(1), 32–40. doi:10.1111/j.1467-9450.2011.00920.x
12 E. XIAO ET AL.

Xiao, E., Shen, J., & Harris, P. (2022). Children with siblings differ from only children in their sharing behaviour. Early Child
Development and Care,192(7), 1007–1019. doi:10.1080/03004430.2020.1829610
Zhang, R., Cai, X., Ran, G., & Xia, Y. (2019). Effects of sibling relationship quality on first-born young children’s empathy.
Studies in Early Childhood Education,08(005), 52–63. doi:10.13861/j.cnki.sece.2019.08.005
Zhou, N., & Qiao, H. (2014). The psychological challenges of the first-born child in a family after the implementation of
the ‘selective two-child’policy. Chinese Journal of Family Planning,22(8), 570–573.
EARLY CHILD DEVELOPMENT AND CARE 13