The aim of this study was to test the feasibility, acceptability and potential efficacy of a childcare-based intervention to reduce total and prolonged sitting time in pre-schoolers. Four centres and 115 pre-schoolers (44 % boys; 4.1y) participated in a 3-month, 2-arm pilot cluster randomised controlled trial. Feasibility and acceptability were assessed through observations and semi-structured interviews. Sitting time, and breaks and bouts of sitting during childcare were assessed using an activPAL accelerometer over a one-week period at pre- and post-test (12wks). EF (inhibition, working memory and shifting) was assessed using the Early Years Toolbox. Intervention fidelity was high for both intervention centres (77 % vs 70 %) and educators reacted positively to the intervention. Proportion of sitting time per day reduced significantly at post-test in both intervention (−5.3%/day,[2.13, 8.50]) and control centres (−6.45 %,[4.20, 8.71]), resulting in a non- significant between-group difference (p = 0.51[2.4, 4.9]). EF scores did not significantly differ between groups (p > 0.05). Modifications to the childcare environment to reducing sitting, particularly the standing workstations, were feasible and acceptable to educators and children. No differences in sitting time between groups were seen; additional changes and longer-term trials are needed to reduce sitting time in pre-schoolers.