Introduction Same-sex parenting remains controversial, with many arguing that it negatively impacts children's psychological and social development. This study investigated the influences of beliefs about the etiology of homosexuality (as either learned or genetic) and ambivalent sexism (benevolent and hostile) on beliefs about children's development in same-sex families. Methods A Chinese sample of 1400 respondents completed an online questionnaire in March-July 2019 and February 2020. The respondents self-identified as gay (490), lesbian (256), heterosexual male (266), or heterosexual female (388). Participants' beliefs about children raised by same-sex parents were measured using the Scale on Beliefs about Children's Adjustment in Same-Sex Families which included two subscales, namely individual opposition and normative opposition. We tested four hypotheses using multiple analysis of variance and hierarchical multiple linear regression. Results Respondents who were male, heterosexual, older, or had stronger beliefs in the learned etiology showed stronger individual and normative opposition to same-sex parenting. Overall, benevolent sexism was related to individual opposition; lesbians and gays' hostile sexism was related to individual opposition, while heterosexuals' hostile sexism was related to normative and individual opposition. Participants' individual opposition was significantly stronger than their normative opposition. Conclusions Chinese lesbians, gays, and heterosexuals hold relatively conservative and traditional beliefs about children's development in same-sex families. Policy Implications Our results suggest a need for legal and policy protection against prejudice and the dissemination of educational material about same-sex families through public service advertising and educational programs.