> Running a family was a brutal two-person job -- and the kids had to dive in to help

In many societies before (say) the 18th/19th Century, extended families would have been the norm, e.g. with elderly relatives living in the same household, helping with food preparation and clothes making. Harvests may have been community-wide affairs. Children would have had to dive in, as you say, but they wouldn't have had school to go to, and there would have been a wide age spread. Maternal mortality (death due to childbirth) was high, and many widowed fathers would have remarried, extending the family further (incidentally this is partly why there are so many step-sisters and step-mothers in folk stories).