WHO Mental Health Gap Action Program (mhGAP) for Improving Child Mental and Behavioral Disorder Service Quality in China

The goal of this clinical trial is to learn if the adapted mhGAP intervention guide (mhGAP-IG) can improve quality of child mental and behavioral disorders (CMBDs) services in China. It will also learn about the implementation of the mhGAP-IG delivered by kindergarten teachers. The main questions it aims to answer are: * Does the adapted mhGAP-IG reduce the symptom severity among children with CMBDs between two and sis years old? * Does the adapted mhGAP-IG reduce psychological distress among caregivers of children with CMBDs? * Does the adapted mhGAP-IG improve mental and behavioral health serivces capacity among kindergarten teachers in China? * How is the feasibility, acceptablity, and what are barriers and facilitators of implementation? Researchers will compare the adapted mhGAP-IG to child healthcare as usual to see if the adapted mhGAP-IG can improve quality of child mental and behavioral disorders services in China. Participants (kindergarten teachers) will: * Complete questionnaires and scales at baseline and at 3-, 6-, 9- and 12- months of intervention; * Receive mhGAP-based trainings; * Deliver long-term child mental and behavioral disorders services (including screenings, referals, follow-up, and physcosocial interventions) to children with CMBDs. Participants (children/caregivers) will: * Complete questionnaires and scales at baseline and at 3-, 6- and 12- months of intervention. * Accept long-term CMBDs management (including screenings, referals, follow-up management, and physcosocial interventions) from mhGAP-trained kindergarten teachers.