I think another way of looking at it is the same way people try to avoid taxes. In China, with the One-Child policy, you would be fined heavily for having more

I think another way of looking at it is the same way people try to avoid taxes. In China, with the One-Child policy, you would be fined heavily for having more than one child (now the limit is two). However there will be scenarios where rural and poorer folks have more children so they will under-report or even neglect to report the size of their children because they don't want to be hit with heavy fines. The disadvantage is however that extra children won't be officially registered and have a hukou and won't enjoy official protections of a Chinese citizen. On the other side of the spectrum, very rich to rich Chinese can pay for the fines and thus might choose to have 2 or more children because the fines are not that expensive to them. I have observed both scenarios when I was in China. Note that there are exceptions to the original one-child policy, ethnic minorities don't need to abide by the one-child policy and rural parents whose first child is a daughter can have an extra child. As well, people from the previous generation who don't have siblings can have two children to make up for the lack of people in their family. Thus the official numbers will have to be taken with a grain of salt in the same manner people and companies report their taxes as there will be individuals with more than one child who under-report to not incur fines.