To examine the relationship between excessive screen time and psychosocial well-being in preschool children, and the potential mediating role of body mass index, sleep duration, and parent-child interaction.

A cross-sectional survey was conducted in Shanghai, China using stratified random sampling design. A representative sample of 20 324 children aged 3-4 years old from 191 kindergartens participated in this study. Parents completed the Strengths and Difficulties Questionnaire and reported the child's time spent on screen exposure, sleep duration, height, weight, and parent-child interactive activities.

Preschool children in Shanghai were exposed to 2.8 (95% CI 2.7, 2.9) hours/day of screen time, with 78.6% (95% CI 77.8,79.3) exceeding 1 hour/day and 53% (95% CI 52.0,53.9) exceeding 2 hours/day. Every additional hour of screen time was associated with increased risk for poor psychosocial well-being. Body mass index, sleep duration, and parent-child interaction mediated the effect of excessive screen time on children's psychosocial well-being, among which parent-child interaction contributed most. Parent-child interaction could explain 28.1% of the effect on total difficulties and 58.6% on prosocial behavior.

Excessive screen time during early childhood exists in Shanghai preschool children. Excessive screen exposure was associated with poor psychosocial well-being in preschool children via a number of mediators, mostly by reducing parent-child interaction.