[jeffreyrogers]

I only know one family with >=8 kids (they have 10) and not that well so I can't really comment on them. I know many with 4-6 kids though. It's true that in most cases the women have a traditional family role (not always though, I know one couple where the wife is a very successful cardiologist and the husband is an athletic trainer). Parental involvement is usually higher in these families than among the 2-3 children, 2 professional parent families I know, mostly because one parent is either not working or working in a reduced capacity.

The eugenics part doesn't match my experience at all. I've never seen any evidence that people who are having large families are motivated by that.

[UncleMeat]

I suspect that parental involvement is higher in aggregate but not when it comes to the time dedicated to each child.

Every younger sibling from a large family that I know was in large part raised by their older siblings.