Watching 60 minutes last night on the fact that in China's new generation, there are 120 boys for every 100 women, due to the one-child-policy and the abortion of girls by those who insist on a son, an obvious answer came to me.
Instead of a one-child policy, have a one-son policy. Ie. after you have your first boy, you must stop. (China actually forces sterilization or insertion of an IUD under surveillance, which I obviously don't think is a great way to do things.)