Kids could play outside alone in the 40s, 50s and 60s too, and child mortality wasn't 1800s they might all die levels. And in some developed countries like germany and japan it still is possible today [0]. Everything that jedberg described wouldn't probably happen.
Around the 70s the workload ratchet started going up, with each decade adding more and more restrictions. Look at stranger things, today it's a bit iffy to let 12 year olds go out biking by themselves to see their friends. In the 80s you could!
[0] https://www.nytimes.com/2018/08/02/reader-center/free-range-...
I think you’re right: in the past, each kid was much less work than they are today. The difference is that you also used to have 6 of them, and used to expect that not all of them might survive to adulthood. This is clearly not acceptable approach in today’s society.