When I was younger I thought that the abbreviation lbs, stood for "illables". I then told people that I weighed some number of illables. It wasn't until middle school that my mom told me illables wasn't a word and it actually stood for pounds.
A childhood belief about speaking

others believed things like this
- I used to think that the abbreviation lb (for pounds) stood for Lilla-blams (like Kilograms)— Jake
- i used to believe (because my dad told me so) that AM stood for "awful music" and FM stood for "fine music"— skydvgrl
- When I was younger I thought MTV was an x-rated station because I thought M stood for Mature.— Aeris
- when i was younger, i thought that people disappeared when i wasn't with them.— Debbie
- In first grade, I thought that if I've never heard of a word before, then it wasn't a word.— Destiny
- When I was little, I thought that if you stood behind the TV, you could see your insides on the screen.— C.W.