If you agree that the world, and the United States in particular, are overpopulated (See Population, Population, Population), then some thought should be given to decreasing the population numbers through good governance.
There are two major aspects to good governance: coming up with a plan or policy, and then actually getting the political consensus necessary to make that policy into law. In this essay I will address the policies that I think would be relatively easy, but still difficult, to make into law in the United States of America.
Tax incentives would be the key element to a realistic program. Currently in the USA, both for state and national income taxes, each child (or dependent, but we are worried here about children) is worth a an exemption. In 2005 the exemption was $3200.
A good meme (slogan) would be "One child is great, two a plenty, a third is too many." If two children is the maximum then population stabilizes over time if life expectancy is also stabile. Some people already have no children or only one child; if the rest are limited to two children, the population trend will head downward. A very small percentage of families having three children might be tolerable.
So if one child is great, lets give a $6,400 exemption for the first child. This would really help families during their child-rearing years when incomes tend to be low and expenses high. The exemption for the second child could be set at $1600. So a two-child family could be better off for taxes than they were in the past. But the family would get no exemption for the third or any later child.
An education campaign should be conducted both to get people to allow this new state of affairs to become law and to get them to cooperate with it. Families that have relatively few children are better able to focus their resources on helping their children. They tend to prosper from generation to generation. Prosperous families also tend to have fewer children than poor families; this is true even in supposedly Catholic nations such as Italy.
To plan families of an appropriate size we need birth control to remain legal and easily available to everyone of an age capable of reproducing.
Some sects will oppose this new policy and likely will defy it if passed. They may avoid paying income taxes, or simply pay their taxes and have lots of children. If they create a mass movement for large families that keeps the population on the upswing, then I would favor sterner measures. But I suspect that there will be relatively few of such cranks and eccentrics. So society can try tolerating them and hoping the children won't be as stupid as the parents.