Mom and Dad were working full time, as were most of the parents in the neighborhood. Over the summers the older kids were supposed to watch the younger ones but the best thing they did was to show us what NOT to do.
We had boundaries beyond which we were not allowed to go and we respected that - but pretty much not anything else. There were no latch key kids - no one locked their houses unless they were going to be gone for more than a day.
We lived next to a lake that had been dredged from a swamp when the neighborhood had been started. Although it was a city park, the city did little to maintain it until the mid 1960s. They didn't even keep the area around the lake mowed so it was quite a jungle.
There were alligators, water moccasins and all kinds of things living in the lake and the jungle around it. We knew to stay away from them and made enough noise they stayed away from us. Still, my first dog was killed by a water moccasin and a neighbor's dog was eaten by an alligator. After that the city dredged the lake again and started mowing it on a regular basis - plus the wildlife people came and caught the larger alligator and took it away. There was a smaller one, but no one told the wildlife guys.
It's amazing none of the kids were ever seriously hurt or got into serious trouble. While we were feral, we policed ourselves and kept entertained without being destructive.
The boy getting buried was the most serious thing that happened and we all helped get him out fast so he wasn't injured. What the adults didn't know didn't worry us - we just took care of ourselves.