China can increase family sizes if they enact the proper policies.
Just look at what the Qin did.
They started cultivating marginal lands.
They accepted migrants that would cultivate these lands.
Once males got into fertile age they they got assigned a plot of land and built their own family unit.
The result was a population explosion which enabled them to unify China.
So it's pretty simple. Just get people an occupation that provides them a decent income and house.
The sooner you do this the better because it will increase the speed of the growth cycle.
Making people have to wait a decade or two before they can own a house is not a good idea.
Just look at what the Qin did.
They started cultivating marginal lands.
They accepted migrants that would cultivate these lands.
Once males got into fertile age they they got assigned a plot of land and built their own family unit.
The result was a population explosion which enabled them to unify China.
So it's pretty simple. Just get people an occupation that provides them a decent income and house.
The sooner you do this the better because it will increase the speed of the growth cycle.
Making people have to wait a decade or two before they can own a house is not a good idea.