The purpose of the research is to examine the early development of children's understanding of social rules, and of the feelings and actions of others within the family. The development of children's ideas of justice, blame, responsibility, authority relation, their differentiation between different kinds of transgressions, and their understanding of the causes of feelings and behavior will be examined by studying the children in a variety of naturally- occurring social contexts with different familiar partners. Fifty second-born children will be observed at home with their mother, sibling, and a family peer, at 33, 39 and at 45 months. Observations will focus upon the children's justifications, excuses, and actions in disputes, their conversations about others, and their cooperation in pretend play. Their reasoning about their own compliant and prosocial behavior, and about that of puppets in a series of puppet-plays will also be assessed in interviews. Processes influencing individual differences in the development of these features of social understanding will be explored, in particular the children's interactions with their mothers, and their siblings. A central aim will be to examine the social understanding, and the use to which these developing abilities are put in the children's different social relationships.