The research analyzes the social challenges of internal migration in modern China. The primary focus is on left-behind children («留守儿童»), i.e. children of rural migrants moving to cities because of work. The author summarizes Chinese sociological studies dealing with the analysis of problem situations in this regard. In particular, the paper describes the pivotal approaches of social and demographic scientists to considering the issue of left-behind children and structuring this social group. Besides, it presents current statistical data and typical case studies. The emphasis is placed on arranging custody and socialization of children whose parents have to leave to work in urban areas. Regardless of the analytical approach or methodology, the researchers conclude that children of rural migrants are vulnerable. The reasons for this situation imply the imbalance in their socialization and maldistribution of resources between urban and rural regions. When the Chinese society faces the increase in the percentage