This paper discusses social and emotional development during childhood and adolescence in the United States, focusing on factors that affect children's prosocial behavior and the role of parents in promoting such behavior. It is argued that changing family structures, including the growth of single parent families and "latch-key" children, along with increasing youth violence and antisocial electronic media, all contribute to the development of antisocial behavior in children. Parents can promote prosocial behavior in early childhood by modeling prosocial behavior, reinforcing prosocial behavior, and providing direct behavioral instruction. During middle childhood, peer rejection, neglect, and loneliness can contribute to antisocial behavior. During adolescence, peer pressure, conformity, social acceptance, and rejection all contribute to social and emotional development. Parents need to maintain a proper perspective, accept outrageous but harmless behavior, and intervene in the case of potentially harmful or dangerous behavior. Overall, parents and other influential adults should focus their energies on understanding children's development, developing prevention strategies during the early childhood years, reinforcing those strategies during middle childhood and adolescence, and being persistent and consistent within the family, school, and community. (Contains 14 references.) (MDM)