Historically, the extended family and neighbors were contributing to raising children. For a couple that doesn't have family close by and lives in a city, parenthood is at least a part-time job.
Part of the issue her is that society, at least in the U.S., has significantly devalued the idea of living close to one's family. Sure, some people don't grow up in economically vibrant areas, but many others move away from family without giving much thought to what they're giving up.
> but many others move away from family without giving much thought to what they're giving up.
I don't know how large of a population that really is. I've found many people move away because their family lives in a place that isn't approachable for them to live in. (e.g. Grew up in the bay area but not with well to do parents - just ones that barely got by. They aren't in careers that afford them $2m homes)
And many move away because they despise them and never wish their children to encounter their family.
I really do think many people give plenty of thought about moving away from family in one way or another. It's their family - they lived with them for something like 18 years. Everyone gives that thought.
Also, mothers didn't have to keep an eye on the kids all the time past infancy. It was fairly common to leave them on their own with other kids to play, only ensuring they're fed on time.
And once they reached a sufficient age (10 or 12), children usually helped the family with their craft.
Before the industrial revolution, what's considered norm today was the norm only for aristocrats.
I'm 37 and the oldest of 4 kids and your first paragraph is for the most part how I grew up. I don't remember my mom following any of us around past a certain age, like 5 or so. She cleaned the house etc. while we played inside or in the backyard. I remember going up the block to the park with my friends without any adults at the age of 10-12 or maybe a little younger.