Well, in most countries, you get external funding from childless people which are paying higher taxes... If people were to pay entirely for the education and health of their offsprings, they would be way less babies in the developed world. And I don't even mention externalities. A human being in a developed country has a big impact on the environment, if people had to pay for it, having a child would out of reach of most.
Which is partly true. Those children will also grow up and pay taxes and contribute to companies which in turn fund the retirement accounts of the elderly community.
