When I was a young teenager, I used to believe that when guys urinated they had to squeeze their penis to make the pee come out. In movies, it showed the men merely holding their penises, not squeezing the pee out.
I found out I had been mistaken when I was playing Barbie's with my friend, and I had made Barbie "help" Ken go to the bathroom.
A childhood belief about weeing and pooing

others believed things like this
- I used to believe that when I went to sleep, my Barbie dolls would make out and plot to kill me.— ClaireRat
- I used to believe when barbie kissed ken a kelly would come out— !!!!!!! loser!!!!!!!!!!!!!
- I used to believe that after I cut my barbie's hair, they will grow again. They've never grown :(— Duda
- I thought nipples disappeared at a certain age because Barbie never had them.Anon
- I use to blame the aliens on my missing barbie dolls.— Lindsay
- I used to believe that if i cut of my Barbie dolls hair that it would grow back.— Zena