The Green Hand...
...was a suburban Chicago legend of a ghoul that (in my neighborhood) hung out near the refreshment shed at the local baseball fields when I was a kid. Most of the older kids passed on the story to us much younger kids to most likely keep us away from the shed. The "green hand" was a manlike thing that was green and would pluck unsuspecting children away if they got too close to the shed at night. I remember being deathly afraid of the shed once the sun went down.
I never knew how the story originated as there were no known child disappearances in my neighborhood at the time. It wan't until years later that I found The Green Man on Wikipedia and figured that this Pennsylvania Urban legend must have made it's way to suburban Chicago and that so many kids had told the story that it evolved into The Green Hand.
I love the idea of how certain games and stories are passed by kids to younger kids without adults interfering. Who taught you how to play "it", "light as a feather, stiff as a board" or "bloody Mary"?