["Review of Development Economics, Volume 30, Issue 3, Page 1600-1620, August 2026. ", "\nABSTRACT\nThe nutrition, health, and cognitive ability of left‐behind children directly determine the human capital level of China's future workforce. The net impact of parental migration on children's development outcomes remains an empirical question. In this article, we use survey data from rural Gansu Province to study the effects of different combinations of parental migration (namely, any parent migrated, both parents migrated, and only one parent migrated) on children's nutrition, health, and cognition. Results from the instrumental variable approach show that left‐behind children perform worse in terms of nutrition, health, and cognitive development compared to their non‐left‐behind peers. Specifically, migration of any parent increased the probability of stunting by 52 percentage points and wasting by 25.7 percentage points, with even stronger effects when only one parent migrates. Migration of both parents, only one parent, and any parent reduced children's probability of good health by 75.9, 73.2, and 54.7 percentage points, respectively. Moreover, parental migration negatively affected children's vocabulary comprehension and working memory, with the greatest negative impact on children when both parents migrated. Children's age moderated the negative effects of parental migration. The mechanism analysis suggests that reduced caregiving quality is a primary channel through which migration harms child outcomes, while remittances provide only partial compensation by slightly increasing food and educational spending. These findings highlight three implications: enhancing direct support for left‐behind children, promoting the effective use of remittances for child development, and reducing the developmental costs of parental absence.\n"]