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.
So many gaming ones.
When mortal kombat was released for consoles, the kids passed the “blood code” for the genesis
When mortal kombat 2 came out, their were so many myths about super fatalities and weird stuff about how street fighter was in it.
Man oh man I could probably have a whole thread just for video game urban legends from the late 90s. That’s when some of your friends had internet, but maybe you didn’t, so there was just enough legit info to make the fake stuff seem believable (looking at you, MissingNo). Luigi in SM64, all sorts of secret Smash 64 characters, literally the entirety of Pokemon.
I wonder if Luigi in SM64 and other games was also a product of memory constraints as some of these games did omit him for that reason specifically and thus presumably had initially been intended to include him before the memory issues came up. If that’s true he may have shown up in very early marketing material and spawned the legends.
Fun fact: In one of the many leaks of Nintendo internal files in the past decade, early source code and the model was found for Luigi in SM64. His inclusion was abandoned very early on in development.