That’s a red herring. A person overlooking 5-15 kids is never going to be able to offer the care a one on one relationship with a mother can. Maybe a nanny might be an analogous alternative but the state will never be able to pay for that.
I am well aware that it is uncommon, coming as I do from a family of eleven children; but the world is much more than America, and birth control is a recent invention. I don't see how you can reasonably claim that one person cannot care for such a number of children when mothers of large families have been doing it for millenia.