This isn't something I thought but another kid did (who was younger than me). We were playing charades, and while I knew how to play it, the kid didn't get it and thought that instead of getting people to guess the words in the title you were supposed to act out what happens in the movie (e.g one of his was The Matrix and he would reel back and wave his arms around like he was Neo dodging bullets.) The other adults tried to explain how it really works but I don't remember if he ever figured it out or not.
A childhood belief about toys

others believed things like this
- I thought a tidal wave was acutualy a title wave because if the wave was big enough it had its own title!— Nate
- I thought the song "Party Time" by Moby was actually saying "heart attack" (this was before I knew the title)— Elviessa
- Even though the title is 'How Bizarre', I always thought he sang "help is on"...Anon
- i thought it was a law that bus drivers had to wave to each other when they passed— ande
- I used to believe that acorns were bullets— Andrea
- Before I knew about death, I used to think people turned back into babies again after they got old. Anon