I used to believe that while 'a couple' meant two, that 'a few' meant three. I thought this at least until I was 8 years old.
Even more embarassingly it was my younger brother who clued me into the fact that 'a few' didn't have to be just three. I argued with him that it even made sense since the word 'few' had three letters in it. Of course, I hadn't considered that 'couple' had more than two letters.
At any rate, my mother settled the argument.
A childhood belief about counting

others believed things like this
- that the word "couple" as in "a couple of items" was synonymous with "several", rather than "just two".— Blair A. Petterson
- My little brother once asked my mother when we past a couple of factories.. if the factories made clouds— nicky
- From the first six letters of this word, I thought that “megalomania” had something to do with megalodons.— Enrico
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren
- I fully believed, up until about 6 years old, that the word 'accident' was a noun that meant 'burnt toast'.— Karl Goetz
- I used to think the olden days came once every couple of yearsAnon