I used to believe that the lyrics "my son John" really were "mice on John" in the nursery rhyme, "Diddle, diddle dumpling, my son John, went to bed with his stockings on..." I found this to be a disturbing way to sleep. And I still have trouble remembering the real words. "Mice on John" just flows off the tongue... :)
A childhood belief about misheard lyrics

others believed things like this
- As a child I used to think that Olivia Newton-John and Elton John were married.
Boy, I was way off.— Lisa - As a child, I thought that Olivia Newton-John was Elton John's wife and Juice Newton's sister.— Connie
- I used to think that Olivia-Newton John was three people like Sharon, Lois and Bram....Olivia, Newt and John— J
- I thought that Olivia Newton John was a group, Olivia Newt and John. — Sam O.
- I used to think that Olivia Newton-John was 3 people: Olivia, Newt, and John— Sally
- I used to think the lyrics to Elton John's Tiny Dancer were "hold me closer Tony Danza."— kstawitz