I was a child in the 70s and 80s.
We his bad behaviour from our parents - not just our own, but that of other children.
It'd never have occurred to me to tell my parents about bad behaviour I witnessed from other children, even when I suffered because of it. There was some kind of honour among thieves type children's unspoken pact.
Bad behaviour happened when parents weren't looking, mostly, and parents didn't want to know in those days. Very much head in the sand/ kids will be kids as long as it doesn't bother the adults.
When I got drunk and misbehaved as a mid teen I made sure my parents wouldn't find out, rather than not doing it. As siblings we protected our parents from finding out about what other siblings did, so they wouldn't worry. That was normal then.
I went to a private school and got very good grades, but my behaviour in some lessons was shocking - I used to lie on the desks in one lesson I remember, I had an overdeveloped sense of injustice and refused point blank to do things I thought were unfair even when punishments snowballed. I walked out of some lessons and went and sat outside on the grass, for no good reason. I think partly because my grades were good and partly because I was a model student in certain lessons, and because I was always verbally polite, my parents were never even called! I think schools call parents in much more quickly now - things used to be dealt with between school and pupil unless they were suspension level serious. There wasn't the opportunity for parents to back kids up! I knew my parents would have sided with school, but it wasn't relevant as pupils didn't have parents between them and school and didn't tell their parents if they were in trouble!
I think the double edged sword of everything being out in the open and parents having vastly more involvement in their children's lives, as well as children being physically with their parents and in adult spaces far more, is the biggest change.
Now we want to know what our kids are up to even if it's inconvenient! This has obvious pros safety wise but also cons in that once hidden behaviours are out in the open, and children are less self sufficient and more dependent, which has a vicious circle impact - parents want the openness but to maintain it condone and overprotect, I suspect.