When I was about eleven, I knew about the periodic table and I thought the expression "exposed to the elements" meant being exposed to the actual elements, like on the periodic table, and I thought, "surely that's everywhere?".
A childhood belief about chemistry

others believed things like this
- I used to believe that there were red and black spiders underneath the table in the toilet.— Phil
- I used to think that the sleep in my eyes at the breakfast table were toast crumbs.— crawford
- i used to believe that a ghost lived under my bed and that a giant lived under our dining room table.— nameless
- I thought the expression "so funny I forgot to laugh" was literal instead of sarcastic— Not so funny after all
- When I was nine, I thought two eleven-year-olds could get married.Anon
- I thought that hydrogen was pure water (since I knew hydro- meant water) and H2O was impure some how— Hexetic