A farmer in a poor country does a simple calculus: every child makes him richer. Children work in the fields and cost very little to raise. Room and board on a farm are almost free. But when you move to the city, the calculus flips the other way. Every child makes you poorer. Your child goes to school, not the fields. Your child has to be fed from the grocery store, which is expensive. Your kid has to live in an apartment, which costs money. So a peasant, once he becomes more urban, wants two kids, not ten.
