We studied the extent of sex-typing across different areas of child functioning (personality, interests, activities) in middle childhood as a function of the traditionality of parents' gender role attitudes and the sex composition of the sibling dyad. Participants included 200 firstborn children (mean = 10.4 years old), their secondborn siblings (mean = 7.7 years old) and their mothers and fathers. Family members were interviewed in their homes about their attitudes and personal characteristics and completed a series of seven evening telephone interviews about their daily activities. We measured children's attitudes, personality characteristics, and interests in sex-typed leisure activities (e.g., sports, handicrafts) as well as time spent in sex-typed leisure activities and household tasks (e.g., washing dishes, home repairs) and with same and opposite sex companions (i.e., parents, peers). Analyses revealed that sex-typing was most evident in children's interests and activities. Further, comparisons of girls versus boys and sisters versus brothers revealed that differences in children's sex-typing as a function of fathers' attitudes and sibling sex constellation were most apparent for children's activities. A notable exception was sex-typed peer involvement; time spent with same versus opposite sex peers was impervious to context effects. Analyses focused on children's sex-typing as a function of mothers' attitudes generally were nonsignificant.