I used to believe that "firearms" meant fire extinguishers, things you use to arm yourself against fires. I couldn't understand why fire extinguishers were illegal in some places.
A childhood belief about speaking

others believed things like this
- I used to believe that the Fire Station was where all fires occurred.Anon
- I used to believe that firemen drove around in their fire trucks and started fires. I wondered why.— Albert
- i always thought it was Grape Balls of Fire instead of Great Balls of Fire— Courtney
- I used to think that being fired meant they set you on fire.
Or they just chopped off your head.Anon - i used 2 think if u lied your pants would catch on fire cus of the sayin "lier lier pants on fire!"— nell
- I used to think that Legal and Illegal meant the same thing (illegal)— Dhruv