Gender-stereotyped beliefs develop early in childhood and are thought to increase with age based on prior research that was primarily carried out in Western cultures. Little research, however, has examined cross-cultural (in)consistencies in the developmental trajectory of gender-stereotyped beliefs. The present study examined implicit gender-toy stereotypes among 4- to 9-year-olds (N = 1,013; 49.70% girls) in Canada, China, and Thailand. Children from all three cultures evidenced implicit gender-toy stereotypes over this developmental period, but cultural differences in the developmental pattern and strength of these stereotypes were apparent. Gender-toy stereotypes were relatively strong and stable across age groups among Thai children and relatively weak and stable across age groups among Chinese children. Canadian 4- to 5-year-old children displayed weaker stereotypes, whereas 6- to 9-year-olds displayed stronger stereotypes. These findings highlight the contribution of culture to children's gender stereotype development. Although gender-toy stereotypes were found among 4- to 9-year-olds in all three cultures examined here, the strength of these stereotypes varies by culture. Furthermore, the previously described increase in gender stereotyping over this developmental period appears to not apply across cultures, thus challenging the conventional view on development in this domain based on prior, mainly Western, research. Public Significance Statement Children from three cultures, Canada, China, and Thailand, evidenced implicit gender-toy stereotypes from ages 4 to 9 years, but cultural differences in the developmental pattern and strength of these stereotypes were apparent. Our findings provide valuable data from two underrepresented non-Western cultures that challenge conventional wisdom-which has been predicated on Western samples-about the developmental course of gender stereotyping.