Ambivalent Sexism Theory draws attention to the ambivalence of sexist beliefs and their key role in the maintenance of gender inequality. Two studies were conducted in order to investigate the development of hostile and benevolent sexism in childhood. A systematic literature review was carried out, reanalyzing literature of the past 9 years of research on gender knowledge in childhood through the framework of Ambivalent Sexism Theory. The findings show that most of the measures applied tap into the dimension of hostile sexism. Those tapping into the benevolent dimensions suggest that children from a young age hold strong beliefs about the complementarity of stereotypes and heterosexual partnership. Second, the Childhood Ambivalent Sexism Measure was developed as a new measure of ambivalent sexism in childhood and applied in a sample of 7-10-year-old Portuguese children. The factor structure obtained allows to distinguish between hostile sexism and two factors of benevolent sexism: protective paternalism and heterosexual intimacy. Results show that children from the age of 7 show high levels of stereotype knowledge and personal endorsement of benevolent sexism. Endorsement of hostile sexism compared to the benevolent sexism is lower, and more so for girls, while for benevolent sexism no gender differences were found. Moreover, the effect of ambivalent sexism on children’s future career aspirations was tested. Girls who show higher stereotype knowledge of protective paternalism also show more interest in professions that require higher levels of warmth as compared to competence. The results are discussed with regard to theoretical implications and recommendations for intervention.