Controversy continues to surround parenting by lesbian and gay (LG) adults and outcomes for their children. As sexual minority parents increasingly adopt children, longitudinal research about child development, parenting, and family relationships is crucial for informing such debates. In the psychological literature, family systems theory contends that children's healthy development depends upon healthy family functioning more so than family structure. From the framework of family stress theory, it was expected that longitudinal outcomes for school-age children adopted in infancy could be distinct among those with same-sex versus other-sex parents (N = 96 families). Similar findings were hypothesized in terms of parent adjustment, couple relationships, and family functioning in comparing same-sex and other-sex parent families. Results indicated that adjustment among children, parents, and couples, as well as family functioning, were not different on the basis of parental sexual orientation (lesbian, gay, or heterosexual) when children were school-age. Rather, children's behavior problems and family functioning during middle childhood were predicted by earlier child adjustment issues and parenting stress. These findings are consistent with and extend previous literature about families headed by LG parents, particularly those that have adopted children. The results have implications for advancing supportive policies, practices, and laws related to adoption and parenting by sexual minority adults.