However, we weren't at the time talking about teenagers but about 9 and 10 year olds (which later turned into 6-10 year olds). Groups of them, entirely unsupervised and free to do what they wanted is probably pretty feral in my experience!
I do believe I said upthread that I played out at 9/10 with children of a similar age and that we were NOT feral. As the poster who lives in Switzerland said of the children in her village, we all knew the adults had half an eye on us and anyone's gran/neighbour would have waded in to restore order had it EVER been necessary (which I don't recall it was). We all knew that anything daft, or stupid, or actually wrong that we did was liable to be reported back to a parent before we'd even got home ('I saw that girl of yours run out across that road without looking and I would have spoken to her myself but they were all that far away...') This ensured that folly and stupidity were carefully avoided, because you just knew that your parents would find out somehow.
The same applied to my own DC. One of them came home reporting, 'A man spoke to me...' 'Oh yes, what did he say?' 'He said, Are you alright, little girl?' 'Who was it?' 'I don't know...' 'You don't know who it was?' 'I don't know his name. But he is Jo's daddy.'
We were a bit older when we got 'naughty' and more prepared to run risks. like sliding open the sash locks of empty (i.e. unoccupied) houses and nipping in to have a look round. We never did any damage. Similarly, we threw knives, but we were sensible about it: we made a target and stayed out of the way.
Re babysitting, my DD has babysat since she was 14. At 15, she babysat several times up until almost midnight for three children, including a baby under a year. Whose mother, incidentally, has a senior legal position and would, I imagine, be fully aware of any legal ramifications.