the world is overpopulated and everyone who wants to have children should require a license to do so (and it should cost a lot - like, a mid-tier job's annual salary).
This would only deter people who would otherwise plan a child. Those people tend to have fewer children in the first place and are more likely to take good care of them. I actually think the best approach to reducing the world's population increase is a heavy investment in education including reproductive education, especially in poorer countries which are the ones still actually growing fast.
Only people with progressive ideologies, willing to educate their children to be better than themselves, socially responsable, solidarity- and community- oriented and willing to work to leave the world a better place than they found it, should have children.
That excludes whole countries and political systems, and that's a good thing.
That would create a generational time bomb. What happens when the now sizeably reduced younger generation has to care for a hoard of old people and pay their pensions?
Ro-butts! And govt procured provisions purchased in bulk if money is tight.
In the 1920s, many Americans who were put to work could not be paid because 'the govt had no money' but from remembrances of those who lived, they never ate better. I'm talking multiple huge fried pork chops per person, etc, but no spending money. It should cost even less to feed seniors, though I'd worry about the diet becoming too inflammatory.
You'll just end up like China with millions of undocumented children, mostly women. Children who are local get to go to school as long as they are registered to live with a local family, so there is no impediment there. Also you will have tremendous flouting of the law unless you create a perfect sterilizing agent that is reversible and deploy it en masse.