Although child care has demonstrated effects on both cognitive and social development, its effects on the acquisition of a theory of mind - an understanding of how one's own and others' minds work - has never been investigated. This process has significance for social development, as understanding others' perspectives facilitates competent interaction. The overall objective of this proposed research is to examine whether and how interactions with peers in child care enhance theory of mind acquisition and therefore social competence. This study will (1) examine whether experience with peers in child care, in conjunction with experiences with siblings and other children, enhances theory of mind; (2) attempt to specify the precise qualities and types of social interactions within child care that predict children's developing theory of mind; and (3) determine whether theory of mind mediates the relationship between experience in child care with peers and social competence. To achieve these goals, this study will add theory of mind experimental tasks to an ongoing, longitudinal study of temperament and child care in which comprehensive measures of socioemotional development and interactions within child care are already being obtained.