I don't think the available data actually shows that. In a wide array of simple societies -- whether the people's primary mode of production is agriculture, hun

I don't think the available data actually shows that. In a wide array of simple societies -- whether the people's primary mode of production is agriculture, hunting, gathering nuts or shaking trees for breadfruit -- it turns out most people are not break even on calorie production until they are about 20! Children probably didn't ever -- or didn't often -- make anyone richer.