Screen time may have a significant association with children's development, yet limited research has examined the specific moderating role of family and child characteristics in this relationship. In this study, we investigated the relationship between screen time exposure and children's development and moderating effects of the family environment (e.g. parental involvement, parenting, and marital adjustment) and child characteristics (e.g. gender, only-child status, urban-rural areas, and left behind) on this relationship. A total of 825 Chinese child--parent dyads participated in the study. The results showed a negative relationship between screen time and children's language and cognitive skills, self-regulation, and self-efficacy and a positive relationship with problem behaviour. Regarding child characteristics, gender moderated the association between screen time and children's self-regulation; sibling status and urban-rural areas moderated the association between screen time and children's problem behaviour. Specifically, screen time had more negative associations with the outcomes of boys, children living in urban areas, and those from only-child households. However, the aspect of the family environment did not facilitate or buffer the relationship. The research verifies and extends the association between screen time and preschoolers' pre-academic and behavioural competence to parental and children's factors and holds substantive theoretical and practical implications for policymakers and family education research in China.