Research Findings: As China scrapped its decades-old one-child policy, the present study examined how family socioeconomic status was linked to preschoolers' self-regulated learning through parental educational expectation and home-based involvement in one- and multi-child families in mainland China. Based on a sample of 1,363 preschoolers involved in the 2018 wave of the China Family Panel Studies, the results showed that Chinese parents of only children exhibited higher levels of home-based involvement in their children's education than did parents with two or more children. Structural equation modeling analyses suggested that parental educational expectation and home-based involvement fully mediated the connections between parental education and self-regulated learning of young children. Moreover, the exact nature of these links differed across one- and multi-child families, which were more complex for children who had at least one sibling. The effect of home-based parental involvement was stronger in multi-child families than in one-child families. Practice or Policy: Findings from this study support the importance of parental involvement in supporting children's learning in the home environment. Further, the findings suggest family support programs should be tailored to the characteristics and needs of the target families in the Chinese sociocultural context.