For years I believed that "giblets" was a made-up word my parents used to describe me and my siblings. My maiden name was Gibbs, so "giblets" obviously meant "little Gibbses". It makes perfect sense. I was in my teens before I figured it out.
A childhood belief about speaking

others believed things like this
- I fully believed, up until about 6 years old, that the word 'accident' was a noun that meant 'burnt toast'.— Karl Goetz
- Until I was about 12 years old I believed that homeless people were made up by my parents to scare me.— Angela B.
- I thought the lines in the sky left behind by airplanes were "sky scrapers". Makes sense.Anon
- when i was 2 or 3 believed that i had lots of animals in my tummy it made sense my mum had baby in hers.— kjc
- my husband believed, until recently, that the word "several" meant seven of something. — sheryl
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren