Based on a panel data from three-round tracking survey of all children aged 6~36 months and their families in County N in West China in 2018， this paper analyzes the impact of the timing of kindergarten enrollment on early childhood development. The results are as follows： 1） Nearly one-third of the sampled children did not enroll on time， with a higher proportion of early enrollment than delayed enrollment.2） Early enrollment leads to an increase in the proportion of children with delayed social-emotional development. There is a U-shape relationship between the children’s enrollment age and the proportion of children with delayed social-emotional development， while delayed enrollment may reduce children’s cognitive abilities. 3） Mechanism analyses suggest that parenting environment is a determinant in the detrimental effects of early and delayed kindergarten entry on children’s early development， and the process of family-school collaboration shows a complementary relationship between family caregiving and school educational investment decisions. Accordingly， it is recommended to implement flexible enrollment policies， improve the caregiving environment for rural children in kindergartens， and enhance support and guidance for family caregiving.