Seems to me very high income families have more kids, or otherwise, families with a stay-at-home mom will have far more children than in two-income households.

Seems to me very high income families have more kids, or otherwise, families with a stay-at-home mom will have far more children than in two-income households. Among the pressures here is a lack of support from grandparents, the affordability of daycare, availability of maternity leave (and by extension, the tolerance workplaces will have for it and how often). It's such that middle-class earners can see a dramatic change in lifestyle if they have more kids, which they don't want to compromise. In poor countries, it doesn't matter: the woman will stay at home, child mortality is high, you won't have contraceptives usually, etc. Another child is another worker (like the old days over here).