Despite the growing body of research on parents' beliefs and practices, relatively little is known about the relations between parents' knowledge of children's development, home‐based activities, and children's early reading and math skills. This study used data from the Early Childhood Longitudinal Study‐Birth Cohort to examine the differences in Asian, Black, Latino, and White children's early reading and math skills at kindergarten entry and whether parents' knowledge of children's development and home‐based activities mediate the relation. Parents' knowledge of children's development was assessed when children were 9 months. Home‐based activities, including home literacy and enrichment, were assessed when children were preschool age. Asian and White children started kindergarten with significantly higher reading and math scores than Black or Latino children. There also were significant differences across groups in the frequency of engagement in home literacy and enrichment activities. Associations between race/ethnicity and reading/math scores were mediated by parents' knowledge of children's development and home literacy activities. Discussion addresses the importance of parents' knowledge of educationally relevant activities and how to engage in such activities to foster children's reading and math skills and to close racial/ethnic gaps. Highlights This paper examined racial/ethnic difference in children's reading and math skills in kindergarten and explores whether parents' knowledge of children's development and home‐based activities mediate the relation between race/ethnicity and children's reading and math skills. By using data from the Early Childhood Longitudinal Study Birth Cohort, this study found that there were systematic racial/ethnic differences in parents' knowledge of children's development, home‐based activities, and children's reading and math skills at the start of kindergarten. Parents' knowledge of children's development and home‐based activities were found to mediate the association between race/ethnicity and children's reading and math skills for all groups.