Or they owned a farm, and 7 or 8 of those kids are already doing significant amounts of farm labor to earn their food. The economics of having tons of kids is radically different when they go from being a cost to a profit in 8ish years instead of from a cost to not a budget item in hopefully 22 if you're lucky.

The US school calendar was based on the realities of this. So was the election schedule, voting on a Tuesday aligns neatly with the schedules of farmers bringing goods to the nearest town for market.