Reviewed are studies describing how forms and features of child care systems can influence the development of social competency with peers during the infancy to preschool periods of development. Interactions between the child care and familial systems in influencing social competency with peers are also examined. Sections of the review focus on children's attachments to adults, caregiver stability, patterns of interaction and socialization at different ages, peer group stability, peer group size and composition, quality of attachment, and the bidirectionality of systems, as well as stress and social support. The review suggests that aspects of the child care system, and of the child care system in interaction with the family system, may influence the development of young children's social competency with peers. Many potential associations between child care and social competency with peers have not been researched. Suggestions for future research are highlighted. Sixty-three references are listed. (RH)