Population migration and air pollution are inevitable problems in the process of urbanisation. With the continuous advancement of urbanisation, the trends in family migration have become more prominent, and children's migration with parents has become an important indicator reflecting the speed, structure, and quality of urbanisation. Our analysis relies on data from China Migrants Dynamic Survey to estimate the effect of air pollution on children's migration with parents. After using the instrumental variables to correct the possible endogeneity, we found that air pollution has a significant negative effect on children's migration with parents. Through further analysis, air pollution mainly affects migrant children by reducing the settlement intention of the migrants, the house purchase tendency in the influx city, and the income level. After replacing the independent variables, using narrow samples, and considering heterogeneity differences, this paper's conclusions remain robust. Therefore, in the process of urbanisation development, it is important to coordinate the relationship between the environment and the population, and it has an important significance to delay the demographic dividend recession and promote sustainable economic development in developing countries.