This actually seems like an unlikely explanation, even though I know it's what people say. Our fertility patterns are converging with Western Europe, including many places with heavily subsidized childcare.
To be clear, this is not to start an argument about subsidized childcare, either for or against. But the European experience suggests that if subsidies have an effect, it's fairly marginal. And these declines are not marginal. This is a cultural and technological shift.
Also worth noting that America's birthrate has for years been unusually high because of immigration, and we had a big secular decline in immigration during the Great Recession. More broadly, rate of growth in immigration seems to have slowed.
