From a recent World Bank research paper on child labour:
Although there is extensive literature on the determinants of child labor and many initiatives aimed at combating it, there is limited evidence on the consequences of child labor on socioeconomic outcomes such as education, wages, and health. Beegle, Dehejia, and Gatti evaluate the causal effect of child labor participation on these outcomes using panel data from Vietnam and an instrumental variables strategy. Five years subsequent to the child labor experience, they find significant negative effects on school participation and educational attainment, but also find substantially higher earnings for those (young) adults who worked as children. The authors find no significant effects on health. Over a longer horizon, they estimate that from age 30 onward the forgone earnings attributable to lost schooling exceed any earnings gain associated with child labor and that the net present discounted value of child labor is positive for discount rates of 11.5 percent or higher. The authors show that child labor is prevalent among households likely to have higher borrowing costs, that are farther from schools, and whose adult members experienced negative returns to their own education. This evidence suggests that reducing child labor will require facilitating access to credit and will also require households to be forward looking.