In order to gain insight into which children aspire towards science-related careers and how these aspirations change over time, 7820 children in England from the nationally representative Millennium Cohort Study were considered. Few children (8.6% of the cohort) consistently expressed science-related career aspirations at age 11 and again at age 14; more children (15.7%) changed from expressing other (non-science) aspirations at age 11 to express science-related aspirations at age 14; other children (12.2%) changed from expressing science-related aspirations at age 11 to express other aspirations at age 14; and the remaining majority of children (63.5%) consistently expressed other career aspirations. Children who consistently expressed science-related aspirations had more advantaged family backgrounds, higher proportions of parents working within science-related fields, higher self-confidence (in science, mathematics, and English), higher school motivation, and higher self-esteem, compared to children who consistently expressed other aspirations. Children who changed towards science-related aspirations were more likely to be boys, children from white backgrounds, and children with higher (at age 14) mathematics self-confidence, science self-confidence, school motivation, and self-esteem. Children who changed aspirations towards science were characterised by increasing science self-confidence, while those who changed aspirations away from science were characterised by decreasing science self-confidence. The findings suggest that further support may be beneficial to help ensure that children's aspirations are not unnecessarily limited by family disadvantage; support after age 11 may also benefit from promoting the feasibility of science careers for all children, regardless of gender and ethnicity.