As children of the '70's, I know we had a whole lot less "supervision" than kids do today. We were sent "out to play"...period. I don't remember ANY parent watching over us. We organized all sort of plans. Some were not so good. LoL
Neighborhoods these days, even on the weekends, are deserted mostly. I wonder if any kids live in the houses I see.
I'll digress a bit, too, thought what you wrote also affects schools.
I had to walk home with one of my sisters until the last day of first grade. On that day, my mom let me walk home alone for the first time. This was a nearly two miles and I had to cross the main street in town. I was barely 6 years old! I felt like such a big kid.
I remember that some of the high school kids used sit on a small bridge in the woods near school and get stoned in the afternoon. They were a bit intimidating to us little kids who were walking home at first. But then they all smiled and made peace signs at us and it was all good. I guess stoners don't really pose much of a threat though (except to the cookie supply). Either way, there is
no way that would happen today.
And of course, the school just let everyone (except the kindergarteners) go free at 3 pm. We all meandered home alone or walked to the school bus alone. No one ever got seriously hurt that I can remember --- in spite of all of our, err, not-so-good plans. Who would have thought that climbing a tree over the height of the phone poles could be dangerous?

My mom's rule was that if I wanted to play at someone's house, I just had to call her by 3:30 to let her know. We didn't have playdates then.
We used to play outside all day. My parents did the same when they were kids. When it was dinnertime or bedtime, my dad would just call for me.
I think the 70s did have some good things to recommend them, really. I let my kids run free as much as I can. People thought I was weird two years ago for letting and 11 and 9 year old go trick-or-treating without supervision! I went all over town when I was 6!