Previous research suggests that early experience of and exposure to the world of work is an important predictor of a child’s future involvement in a STEM career. Many interventions have focused on those in secondary education age 11 years and above. Far fewer interventions have explored the impact of STEM outreach engagements among younger age groups. This study investigates the impact of a project that delivered career-driven STEM interventions on young children’s (7–10 years old) career knowledge and perceptions over time. Using an action research approach, this study outlines 10 distinct features for designing child-centred STEM interventions. These were delivered in 6 primary schools across North-East England over a 2-year period. A STEM Career Knowledge and Aspirations Tool was used to collect data to evaluate the impact of these interventions. Children sorted 30 job cards (mix of STEM and non-STEM) into jobs they knew, and also into jobs they would like to do. Baseline data and follow up data were collected in 2015 (n = 352) and 2017 (n = 356). Data analysis suggests the sustained interventions had a particularly positive effect on girls. In 2015 prior to the interventions, girls were significantly less likely than boys to know the following STEM jobs: surveyor, technician and game tester. In 2017, following the sustained intervention, there was no significant difference between boys and girls. Furthermore, one of the STEM jobs, Engineer, showed the greatest increase in the percentage of boys and girls that wanted to do it in 2017 compared to 2015.