I used to believe that Jane Jetson was supposed to be an alien. After all, she had those weird musk-ox-like horns!
I didn't realize until I was about 28 that those "horns" were just supposed to be her hair. Duh.
She was WAY more interesting when she was an alien!
A childhood belief about cartoons

others believed things like this
- I thought the ball-headed person in the Bic logo was an alien and communicated using alien-like noises.Anon
- That unicorns were real. They simply had invisible horns that only people with special eyes could see
— Katie - Oh oh, I'm an alien, I'm a little alien...
Legal maybe?— Marina - I didn't understand about boiled eggs until my Mum explained I wasn't supposed to eat the shell as well.— Chris
- I didn't know whether nail files were supposed to make your nails sharper or duller.Anon
- I used to think that my cat was an alien that had come to teach me how to be good!— laz