Childlore is folklore passed directly between children, without the input of adults.
https://en.wikipedia.org/wiki/Childlore
Stuff I can think of off the top of my head are paper fortune tellers, summoning Bloody Mary/the candyman, the cool S, parody songs like “Jingle bells Batman Smells” and “Joy to the world, the teacher’s dead” etc.
This stuff has intrigued me since, well since I was a kid. I always wondered where they came from. I never saw adults doing that stuff, so I figured another kid had to have come up with it.
I middle/high school the best sub was rumored to live out of the back of his station wagon and had cardboard boxes to extend the back of it for extra shelter. It didn’t help that the man embraced the rumor.
He once shared some pie with me when I was having a small breakdown in an empty room senior year due to my severe depression and from being bullied severely. He just offered me pie and we sat in silence and each ate a piece and then went on our way. It was nice.