The ambitious expansion of social health insurance in China has played a crucial role in preventing and alleviating poverty caused by illness. However, there is no government-sponsored health insurance program specifically for younger children and inequities are more pronounced in healthcare utilization, medical expenditure, and satisfaction in some households with severely ill children. This study assessed the effectiveness of child health insurance in terms of alleviating poverty caused by illness. Data were collected from two rounds of follow-up surveys using the China Family Panel Studies 2016 and 2018 child questionnaires to investigate the relationship between child health insurance and household medical impoverishment (MI). Impoverishing health expenditure (IHE) and catastrophic health expenditure (CHE) were measured to quantify "poverty due to illness" in terms of absolute and relative poverty, respectively. Propensity score matching with the difference-in-differences (PSM-DID) method, robustness tests, and heterogeneity analysis were conducted to address endogeneity issues. Social health insurance for children significantly reduced household impoverishment due to illness. Under the shock of illness, the incidences of IHE and CHE were significantly lower in households with insured children. The poverty alleviation mechanism transmitted by children enrolled in social health insurance was primarily driven by hospitalization reimbursements and the proportion of out-of-pocket medical payments among the total medical expenditure for children. Children's possession of social health insurance significantly reduced the likelihood of household poverty due to illness. The poverty-reducing effect of social medical insurance is most significant in rural areas, low-income families, no-left-behind children, and infants. Targeted poverty alleviation strategies for marginalized groups and areas would ensure the equity and efficiency of health system reforms, contributing to the goal of universal health insurance coverage in China.