Here's some more silly stuff I thought as a kid:
- I used to call Night on Bald Mountain "the Sonic song" because it was used in the theme song for Adventures of Sonic the Hedgehog.
- This wasn't really when I was a young kid (I was probably 12 or 13), but when I first started watching Littlest Pet Shop, I thought Vinnie's name was Lenny.
- I also wasn't a young kid when I thought this, but back when I saw the first promo for Steven Universe, I thought Garnet was a boy. (Not that she's a girl, either, since gems are technically genderless, and... I'm rambling, aren't I...)
- In Super Mario 64, when Mario would say "let's-a go!" when you started a level, my cousin and I thought he said "a pickle!".
- When I was young, I thought the red thing on Yoshi's back was a giant button. Probably because I had a Happy Meal toy of him that made sound when you pushed his back. It wasn't until years later that I found out it was supposed to be a shell.
- I used to think that Care-A-Lot (the home of the Care Bears) was real and was actually up in the clouds, and that the Care Bears were up there looking down on everyone.
- I was disappointed by the Disney Channel show Even Stevens when I was little because I thought the whole show would be animated in stop-motion like the intro.