The future world population can be predicted fairly far in advance (many decades) because it depends on current fertility rates and the fact that life expectancy doesn't change drastically. And even fertility rates follow predicable trends.
There is no reason, why artificial womb, possibly with multiple selection box for genes, is not a very realistic possibility, along with state funded child rearing services. (see Norway)
2. Most people actually want children. Getting someone to actually procreate with that will share burden.
3. Investing in children should hel to fund future pension payments. There is pretty good case for self-interest.
4. China won't care, neither will Russia or other parts of world.
5. Countries that will do that will have a better outcome than countries full of retirees. Unless AI takes over, natural selection will take care of rest