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.
Hold your breath when you pass the graveyard, or go through a tunnel.
Lift your feet off the ground when a vehicle you’re in goes under the train tracks.
If you sharpen a pencil really sharp, you can stick it into a ceiling tile and it will stay there.
Chew up some paper and you can spit it at someone through a straw as a spitball.
How to fold a paper fortune teller, and play it. For some reason my classmates labeled it with the different kinds of sex acts we had heard of but didn’t really understand. (Kissing, sex, 69, blowjob…)
How to play MASH.
How to play tag.