I used to believe that you had a 'swear line' in your body. Each time you swore, you filled up a space on the line. Once you ran out of space, you died! Luckily Biology cleared it up.
A childhood belief about swearing

others believed things like this
- i used to think that vacuum cleaners had little piece of space inside them because space is a vacuumAnon
- I used to believe that a "punch line" meant a line of people waiting to dip punch from a punch bowl.— Sheila
- when i was little, i used to believe that airplanes goes out of space.Anon
- I used to believe that babies came from outer-space. :)Anon
- Me and my friend used to believe that space was in God's belly— Lia
- When I was really little I used to belief that fireworks dropped out of the sky from outer space.— davesgrl2001