When I was around 7 or 8, we moved to a house that had chickens, roosters, horses and a few ducks. My mom told me that the way eggs turn into baby chickens is that the rooster fertilizes the eggs. (I already knew how OTHER animals with "live births" got pregnant. I never really thought much of it, but I took this to mean that the chicken lays the eggs, and then the rooster sits on them and does the deed.
I skipped grades in school, and my IQ is QUITE high (not as high as it was when I was a kid, though!) Yet I didn't actually "find out" how baby chickens get "into the egg" until I was a young adult...
A childhood belief about birds

others believed things like this
- I used to believe that only brown eggs came from chickens. I thought white eggs were made at the store— Destiny
- I used to believe that chickens reproduced A sexually and that roosters were just handicapped chickens. — Teena Strang
- My partner's Mum thought that pigs layed sausages just like chickens lay eggs.— Bunny
- I used to believe that like chickens lay eggs, pigs laid sausages...Anon
- I believed that chickens pooped eggs (male and female)— WHAT-A-Doodle-WHO??
- I used to beleive that eggs were actually poop from chickens, and that eating it would make you throw up.Anon