Using data from the 2000, 2010, and 2020 National Population Census of China, this study uncovers evolving trends in the experiences of children in family structures reshaped by China's massive internal migration. We develop a new framework to examine family structures from the census data, which facilitates a detailed exploration of family splits as a result of migration. Our results show a significant surge in the proportion of children in migrant families and the trend of children on the move. While the number of left‐behind children far exceeded that of migrant children in 2000, the picture became the opposite in 2020, signifying an enhanced capacity and inclination for migrant parents to bring their children to migration destinations. This shift has also engendered a more heterogeneous population of children in migrant families. Notably, a subgroup warranting particular attention is that of "left‐behind child migrants," those moving to proximate towns or cities without both parents. This emergence blurs the traditional urban–rural dichotomies and underscores the intricacies of a family split within the migrant population. Finally, we reflect on the significant role of educational aspirations and obstacles that influence these migratory patterns. [ABSTRACT FROM AUTHOR]