Some 61 million children were left behind by migrant parents in China in 2010–14, or almost 22% of the country's children (see go.nature.com/clylrn; in Chinese). This side effect of urban development is seriously affecting the mental and physical health of those abandoned juveniles who are uncared for. We urge China's government to weigh this social damage against economic gain and to take steps to mitigate it.

There were 274 million Chinese migrant workers in 2014 — an unprecedented number. Evidence is increasing for the adverse effects of such upheaval on some children's physical, psychological and social development (Q. Li et al. China Econ. Review 36, 367–376 (2015); G. Ding and Y. Bao J. Child Psychol. Psychiatr. 55, 411–412 (2014)).

Despite China's great economic achievements, its childcare services remain underfunded and underdeveloped. There is an urgent need for policy reform and strategies to tackle the problem. These include the development and enforcement of family interventions, community support and schooling improvements.