Overcoming gender occupational stereotypes is a major educational objective in removing barriers to children's future career ambitions and employment aspirations. Yet, the mechanisms that underlie the development of occupational stereotypes in school-age children remain unclear. This questionnaire study investigates the developmental relationship between two possible factors contributing to occupational stereotype development, perceptions of occupational gender ratio and personal beliefs about occupational competence, across the primary school years. One questionnaire assessed beliefs about the occupations held by men and women, by asking 195 children, aged 6 to 11 (UK Years 2 to 6), to report on the gender ratio of 24 occupations (e.g., who does a specific job) on a 5-point Likert scale (only males, mostly males, both, mostly females or only females). A second questionnaire assessed stereotyped attitudes by asking 194 children of comparable age to judge the competence of men and women (e.g., who can do a specific job very well) on the same scale. We found that children across age groups predominantly assigned men and women to traditionally male and female occupations, respectively, both in terms of perceived distribution and competence. However, while the perceived distribution of men and women remained stable across the sexes and age groups, stereotyped responding for competence was lower in girls than in boys, and decreased with age in both sexes for traditionally male and gender-neutral (but not for traditionally female), occupations. Some occupations which have become less gender-segregated in the workforce (e.g., Doctor, Head teacher), are also becoming more gender-balanced in children's beliefs. Taken together these results suggest that children's occupational stereotypes are influenced by developmental differences in children's understanding of gender, as well as perceptions about what jobs women and men have. We conclude by discussing practical implications for targeted interventions aimed at reducing occupational stereotyping in children.