Measurement and data analysis
We evaluated the children’s social-emotional development using the Ages & Stages Questionnaires: Social Emotional, Second Edition (ASQ: SE-2), a caregiver-reported screening tool to identify social-emotional problems among children aged 1-72 months; The ASQ: SE-2 has been introduced in many countries and is widely used in research and clinical settings. It has been adapted to the Chinese context and approved as a reliable tool for assessing the social-emotional development of children aged 0-6 [We trained four graduate students to help caregivers log into the ASQ: SE-2 electronic system which provides uniform illustration and audio-visual materials. Raw data were automatically uploaded. Child demographic characteristics (including gender, age and order of birth) and maternal demographic characteristics (including education, marital status, attendance, caregiver’s satisfaction toward intervention and socioeconomic status) were chosen as control variables. All questionnaires were administered by the GoodData software (GoodData, Beijing, China) using an Android system. We set the range and logistics of each response in advance to guarantee data accuracy completeness.According to the rules of the intention-to-treat (ITT) analysis, we performed the data distribution before the data analysis. For the descriptive analysis on the children (age group, gender, and birth order), parents (i.e. education, age, and stay-at-home parent) and the family’s socioeconomic status (i.e. annual income in 2018, vehicle ownership, and household appliance ownership), we used 