I used to think there was a monster under my bed and I would never stand next to my bed after nightfall because I thought a creepy hand would reach out and grab one of my ankles. (When it was time to go to bed, I used to take a running jump.)
Gahan Wilson once did a hilarious series of cartoons about childhood myths. My favorite: “If you make a face at someone and get slapped on the back, your face will freeze with that expression for the rest of your life.”
My myth: there were strip mines in the hills around our town in NE Ohio and the excavators worked around the clock, their engines making a noise like galloping. That was the Headless Horseman riding through those hills and he would snatch any kid whose nightstand light was on, right out through the window. I read my comic books with a flashlight under several blankets, for months.
;^)