Sample size and power calculation
The Care Group Intervention is designed to increase children’s social-emotional development by 0.35 standard deviations (SDs). Assuming a 95% confidence interval (CI) and a power of 0.80, we calculated the minimum sample size as 102 per group using the G*Power 3.1 software. We estimated a 90% valid data and 80% follow-up rate. We thus aimed to recruit 142 participants in each group, with a total 284 participants (142 × 2).