This study examined the role of family cultural values as moderators of the association between family relations and the adjustment of young children. Fifty-five families of Mexican descent with young children enrolled in Head Start programs in the Southwest participated. Mothers provided information about closeness of the mother-child relationship, warmth in the sibling relationship, child behavior problems, and familism and simpatia, or two cultural values associated with families of Mexican origin. The children's preschool teachers provided information about child emotional adjustment and social functioning with peers six months later. Familism was found to act as a moderator, whereby warmth and closeness in family relationships coupled with the endorsement of a family cultural value that complements these relationship characteristics was associated with more optimal functioning in preschool classrooms. Results demonstrate the need to evaluate family cultural values or beliefs systems in conjunction with qualities of family relationships as determinants of children's developmental outcomes. Specifically, familism emerged as a family characteristic capable of promoting young children's adjustment within and beyond the family context.