Research Findings: Since 2011, China has started to loosen its tight on the One-child Policy (OCP), which has impacted parent's child-rearing beliefs and the provision of home learning environment that constitutes family environment. Utilizing parent-reported data on 4,364 zero- to eight-year-olds from the China Family Panel Study (CFPS, wave 2014) nationwide survey, we examined the relations among family structure, family environment, and child social competence. Analysis indicated that there were significant differences between only- and non-only-child families in terms of their age, urbanicity, family income, and family environment. The three-step latent profile approach revealed two family environment profiles: "Modern Family Environment" (12.4%) and "Traditional Family Environment" (86.6%), and that child singleton status was a significant predictor of profile membership. Bootstrap mediation analysis revealed that family environment profile fully mediated the relation between family structure and child social competence. Practice or Policy: The results highlighted the importance of providing a stimulating and supportive family environment, especially in families with multiple children. It also informed policymakers and practitioners of possible pathways to support young children's development by enhancing the quality of the family environment.