Left behind or together? Urban-rural institutional barriers, city size and child co-migration with migrant families in China

Urbanization worldwide creates institutional barriers that systematically separate migrant families, hindering population mobility and undermining migrant social integration and inclusive urban development goals. How specific urban contexts and policy designs shape these outcomes remain insufficiently quantified. Here, using multilevel models on national survey data from 119 Chinese cities, we systematically disentangle the distinct associations of different institutional barriers on parent child co-migration patterns. We find that educational barriers are the primary institutional constraint on family separation, reducing co-migration odds by up to 96% in the strictest cities, far exceeding the impact of parental settlement policies. Accounting for these barriers reveals a critical dual effect of urban scale: the net pull of large cities becomes positive, with a 10% population increase raising co-migration odds by approximately 2%. We also identify a constrained household compromise, where maternal non-employment is strongly associated with a more than 6-fold increase in co-migration odds, reflecting a forced reliance on traditional caregiving roles. These findings reveal a covert paradigm of urban spatial sorting where cities extract labor while hindering social reproduction. This provides cities worldwide with an evidence-based framework for inclusive urban governance, demonstrating that true social integration requires targeted educational reforms rather than mere settlement policy changes.