I used to think that there was a line in the Box Tops song "Cry Like A Baby" that was "When I think about the good lucky caveman, I cry like a baby." (The line actually was "When I think about the good love you gave me, I cry like a baby.")
It made perfect sense in my head--the singer envied cavemen since they got to live in a world unsullied by pollution. I made up my mind that the song was an environmental message.
A childhood belief about misheard lyrics

others believed things like this
- when i was 2 or 3 believed that i had lots of animals in my tummy it made sense my mum had baby in hers.— kjc
- I used to believe that dumplings were made from baby ducks. — Sarah
- My friend used to believe baby oil was made from babiesAnon
- I used to believe that Chicken Mc Nuggets were made from baby chicks— Sara
- I thought baby oli was made from pressed babies.Anon
- on "highway to hell" i always thought it goes "baby see, baby do" instead of "hey satan, payin´ my dues"— Miss Understood