Two studies were designed to investigate the relation between emotion socialization variables, social cognitive knowledge, and children's social competence. In Study 1, the expression and situation knowledge of 46 low-income preschoolers were assessed. Peer competence within the preschool setting was also evaluated. Mothers completed questionnaires designed to assess negative emotion socialization practices. Results showed that maternal reports of their emotion socialization practices were related to sad and angry situation knowledge. The aggregate measure of situation knowledge predicted peer competence. In Study 2, 41 low-income preschoolers were observed in a caregiving situation with their younger siblings. The preschoolers' rate of caregiving behavior was recorded and measures of their situation knowledge, emotional role taking, and caregiving script knowledge were obtained. Mothers completed emotion socialization questionnaires. Situation knowledge was the social cognitive variable that predicted sibling caregiving behavior. However, only the maternal emotion socialization variables were directly related to sibling caregiving behavior. These findings highlight the importance of situation knowledge and emotion socialization practices for low-income children's social competence with peers and siblings and provide much needed information on the social development of low-income children.