I used to believe that the definition of "party pooper" was "a person who poops a party." I guess that was because "party pooper" has the word "poop" in it. But now, I know that being a party pooper has absolutely nothing to do with pooping.
A childhood belief about speaking

others believed things like this
- I used to believe "Pedestrians" was a political party like Democrats or Republicans.— August
- I used to believe the living room furniture would party after we all went to sleep.— Ellen
- I used to believe my dolls would come to life at night and have a party while i was sleeping. — phil(:
- I used belive when all the people were out of the house. All the inanimmate objects would have a party.— tracy
- I still belive that when a I sleep, my toys would have a party and play with each other until dawn.— Meah
- I thought the song "Party Time" by Moby was actually saying "heart attack" (this was before I knew the title)— Elviessa