The accumulation of children's human capital is a cornerstone of Chinese-style modernization. Exploiting the phased implementation of the Urban Resident Basic Medical Insurance (URBMI) scheme as a quasi-natural experiment, this study employs a cohort-based difference-in-differences(DID) model and uses data from the 2014-2022 China Family Panel Studies (CFPS) to systematically examine the medium- to long-term effects of early-life health insurance on children's human capital accumulation and its underlying mechanisms. The results show that early-life insurance coverage significantly improves health outcomes and educational attainment during adolescence (ages 10-19), with stronger effects observed among those who gained insurance at younger ages. Mechanism analysis reveals that URBMI enhances access to healthcare for children aged 0-5, reduces illness incidence, increases paternal labor supply and household income, and promotes long-term household wealth accumulation and education investment. These findings provide theoretical support and policy implications for optimizing child health insurance schemes, improving the efficiency of public investment in human capital, and advancing common prosperity.