The circadian system is constituted by a set of structures that generate, coordinate and synchronize the sleep-wake rhythm and the rest of the circadian rhythms, both internally and with the environment, synchronizing the phase of the different rhythms with the natural light-dark cycle. This system is composed of: central pacemakers, peripheral oscillators, a molecular clock, retina, pineal gland and pathways to transmit the input and output signals. During the first semester of life the different circadian rhythms appear and mature in the infant. It is important to highlight the influence of synchronic mother-child interaction as a preventive element of chronodisruption. In this aspect, the role of the primary health care pediatrician as a health educator is of enormous importance. Each individual has an endogenous circadian rhythm, in such a way that depending on the moment of activity and rest, of sleep and awakening, different variations may exist (Chronotypes). There is a morning chronotype that falls asleep and wakes up very early and that is more alert, with more capacity for work and exercise in the morning and an evening chronotype in which all these processes are delayed because they fall asleep and wake up very late. The majority of the population is somewhere in between the two chronotypes.