Social capital has been shown to be positively associated with a range of health outcomes, yet few studies have explored the association between mother's social capital and children's health. This study examines the relation between mothers' access to social capital (via participation in community activities) and child health. Instrumental variable estimation was applied to cross sectional data of the Indonesian Family Life Survey (IFLS) 2007 which consist of face-to-face interviews among the adult population in Indonesia (N(mothers) = 3450, N(children) = 4612, N(communities) = 309, and participation rate at 92%). The findings show strong evidence for the causal flow running from a mother's social capital to her children's health. All instruments are highly correlated with mothers' social capital but uncorrelated with child health. The findings are also robust to individual and community characteristics associated with child health, and suggest that enlarging mothers' social capital through various community activities is a particularly relevant intervention for reducing child health disparities in Indonesia.