My ex-girlfiend's daughter was about 3 or 4 years old and her mother also had a 8 month-old baby boy at the time.
In conversation, I referred to the baby as a boy. The daughter corrected me and said "That's not a boy, that's a baby!"
She wouldn't believe me when I tried to explain that he was a baby boy. In her mind, it was either a boy or a baby, it couldn't be both, and clearly it was a baby.
A childhood belief about getting older

others believed things like this
- My daughter thought bumblebees were baby hummingbirds. — Carolyn
- on "highway to hell" i always thought it goes "baby see, baby do" instead of "hey satan, payin´ my dues"— Miss Understood
- That because Gerber Baby Food had a baby on it real babies were put in there. Thanks a lot cousin!— Nicole
- I used to believe that a baby shower was a tiny bathtub with a showerhead just for the baby.— Amy
- when I was little I used to think you had to have a baby before you got married!— Supergirl
- I used to believe that sparrows were baby pigeons— greenpolyester