When I was growing up in Southern California, there was this used car lot that would play commercials on TV. They always started out with "This is Cal Worthington and his dog Spot." Then the theme song would start. For years I thought the chorus of the song was "pussycow, pussycow, pussycow" instead of "go see Cal, go see Cal, go see Cal". For years I wonder what the heck a pussycow was.
A childhood belief about misheard lyrics

others believed things like this
- I thought the song Hotel California by the Eagles said "Welcome to Oakdale California— JewLea
- I used to think that the actors on tv shows sang the show's theme song.Anon
- Until I was about 15, I beleived my Father was the person who sang the "Cheers" TV Show Theme Song.— Dustin
- I used to think that the chorus of "mountain song" by jane's addiction was in a different language— nothing'sshocking
- I swear I heard a Disney Channel/Radio Disney song where the chorus was a repeated “Damn it”— SpengBab
- I use to think that Bruce Springsteen's song "growing up" was called "throwing up"— glowworm