I used to believe that part of the words to Handel's Messiah were "Bounce the ball." It wasn't until years later, after I came to know Jesus personally, and started reading the Bible that I realized they were quoting from Isaiah 9:6
6 For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called WONDERFUL, COUNSELLOR, The mighty God, The everlasting Father, The Prince of Peace.
KJV
A childhood belief about hymns

others believed things like this
- I used to think the song"jesus, oh what a wonderful child so holy, meek and mild" was "so holy, Mickey Mouse"— Stephani
- I used to think volleyball was actually called "ball-y ball"Anon
- When I was a child I used to belive that my father had forever been a 40 years old man.— Nicola
- How could Baby Jesus be born on Dec 25th, get tall, grow a beard and then die, all by Easter. Whew!— Joe
- When I was a kid, I believed that bible school was "beauty school", and called it that all the time.— Dana
- When i was child, i used to think my father was my father christmas.— BeB's