Having 0-2 happy children vs having 8-12 children running around dirty, hungry and naked.

Yup. People naturally choose the former if they can, but a country with fewer people is weaker and may become poorer.

So it’s a government’s job to make it affordable to have children.

This part of reality is explained best via logic which may seem a bit fascist, but it does exist. It’s not a good thing to be eaten.