Early childhood centres are important places for physical activity promotion in young children, considering the amount of time that children spend at childcare centres. The aim of this study was to train early childhood educators on physical activity promotion in children. Participants included 150 preschool children (75 female; M age = 46.15 months; SD = 5.02) from 7 early childhood centres located in Athens, Greece. Early childhood educators (N = 16; n[subscript intervention] = 9, n[subscript control] = 7) were allocated to intervention (n = 4) or control groups (n = 3). Teachers were provided with a learning workshop consisting of lectures and practical sessions. Children were fitted with pedometers mounted on the right hip during children's stay at the childcare centre on two random days before and after the intervention. A mixed 2 (group: intervention vs. control) × 2 (gender) × 2 (time of testing: before vs. after the intervention) experimental design with repeated measures on the latter factor was used. The number of children's steps was set as the dependent variable. Results showed a significant main effect of gender, with boys having more steps than girls but no differences between the two experimental groups. Training of early childhood educators, reliable assessments of physical activity and fidelity measures of compliance with physical activity are indispensable. Professional development of longer duration may provoke substantial changes in children's daily routine to include more opportunities for physical activity participation.