I had a toy called Learn Through Music which had cartridges with pictures that would go into a toy with a touchscreen and buttons. The cartridges would be based on popular children's tv shows. My younger siblings would play with it for years. Now here's the belief!
The demo cartridge had samples of the Spongebob cartridge, one slide had him singing about what over, under, and through mean. Part of the lyrics (to the tune of Johnny Comes Marching Home) were:
"Under means go below below, below. Over means go above above, above."
I thought he was singing "underneath" and "overneath"! I knew that overneath wasn't a real word, I thought it was just part of Spongebob's usual silliness. I only realized my mistake in recent years!
A childhood belief about misheard lyrics

others believed things like this
- When i was a kid, i thought that nematodes would eat our house like in one episode of SpongeBobAnon
- I thought Spongebob Squarepants was a piece of Swiss cheese.— Melanie
- I used to believe that the video clip are realized in one time and the singers are singing with to the music Anon
- I used to think that Spongebob took place on LAND.— Eeveelover8632
- i used to believe i was spongebob squarepants in a previous life.— former sponge
- I thought Hurricane Dennis (in 2005) and the character Dennis from the Spongebob movie were related somehow.Anon