Developing countries are experiencing unprecedented levels of urbanization. Although most of these movements are motivated by economic reasons, they could affect the human capital accumulation of the children who follow their parents to the cities. This paper estimates the causal effect of permanently migrating as a child from a rural area to an urban area on human capital outcomes. To our knowledge, this paper is one of only several papers, especially in the context of a developing country, which is able to estimate the causal effect of migration. We utilize a recent survey of urban-rural migrants in Indonesia and merge it with a nationally representative survey to create a dataset that contains migrants in urban areas and non-migrants in rural areas who were born in the same rural districts. We then employ a measure of district-level propensity to migrate, calculated from the Indonesian intercensal survey, as an instrument. We find that childhood migration to urban areas increase education attainment by about 4.5 years by the time these individuals are adults. In addition, the childhood migrants face a lower probability to be underweight by about 15 percentage points as adults. However, we find no statistically significant effect on height, which is a measure of long-term nutritional intake, and we only find a weak effect on the probability to be obese. Therefore, our results suggest a permanent, positive, and large effect of childhood migration on education attainment and some health measures. In addition, our results can rule out any negative effect on health.