A set of infant features (large forehead, large and low-lying eyes, and bulging cheeks), were described in classical ethology as social releasers, simple stimuli that evoke a stereotyped response, in this case nurturing. We assessed the attractiveness of such features in the faces of dogs or cats (adults and young) or teddy bears or human infants, and also related these preferences to the degree of attachment to a pet. Overall, faces with the infant features were rated as more attractive than those without. Human infant faces were no more attractive than those of kittens or puppies. Pet faces were rated as more attractive by pet owners than non-pet owners, regardless of whether the faces had infant features. A preference was also found for infant features in teddy bear faces. Women showed higher ratings than men for pets with infant features, but not for human infants or pets without infant features. Parents found human infants’ faces more attractive than did non-parents, but there were no differences for other faces with infant features. Preferences were to some extent specific to the participant’s preferred pet species. Owners who were more strongly attached to their pets showed stronger preferences for photographs with infant features. The findings are discussed in terms of the concept of social releaser, and its part in the development of attachment to a pet species.