That's just a silly assertion. Many developing countries have little to no subsidies in regards to children and yet their birth rates are higher.
Better medical treatments and lack of wars are not child subsidies.
Better medical treatments and lack of wars are not child subsidies.
Lower education and religion is probably the biggest cause for these higher birth rates. In the victorian era, people would simply not get married if they didn't have the means to raise children, and they would be childless, and there was nothing strange about that. To give subsidies for everyone to have children comes from the post ww2 politics.