I used to think the snowman in the song, "Winter Wonderland", was "parse and brown". ("In the meadow, we can build a snowman, and pretend that he is Parson Brown.") I didn't know what "parse" meant, nor understand why anyone would want to build a snowman from dirty snow.
A childhood belief about misheard lyrics

others believed things like this
- Brown or otherwise non-white snow was snowman poop. My kids believe it too!— Dellio
- I used to believe I could grow up to be a snowman.Anon
- When I was little, I thought he was called the "Abdominal Snowman" instead of "Abominable."Anon
- i used to think the song "walking in a winter wonderland" was "walking in a womens underwear"— stephen s
- My mom always used to tell me that brown eggs came from brown chickens.— Taylor
- when i was younger, i used to believe when i slept a other world was buildAnon