Thanks. I think humans are biologically wired to worry, so they will worry about the biggest risk currently available, which might be fairly small.

Also, small families are themselves a product of both lower mortality and wealth so the causation is complex. Without reliable savings or social security, children were the means to not end up destitute and starving in old age or through sickness. If you live in a poor place, you will actually see this happen and a culture will evolve around it. There are still great reasons to have kids, of course, but it's no longer driven by the need for insurance. A "barren" woman is not a visible failure in the affluent world - it may be a lifestyle choice.