I used to think that "cross-eyed" meant that people had X's for eyes, like dead people in cartoons.
A childhood belief about eyes

others believed things like this
- I used to believe that a street sign that read "Dead End" meant that there were dead people buried there.Anon
- When I was younger, I believed that squinting in a storm would make you cross-eyed... forever.Anon
- I used to wonder why people didn't have outlines like they did in cartoons.— Anna
- I used to believe cartoons were real people and animals. They were just wet.— Wendy
- I used to believe cartoons where real people. You can imagine how that went... — Emma
- When I was a kid I used to believe that cartoons were people dressed up in special costumes.— Sarah-Jane