When I was about 4 years old I used to believe that light colored foods (like popcorn, mashed potatoes) were "processed" into urine (because it was light colored) and dark colored foods were "processed" into poop (because it was darker). I didn't think solids or liquids had anything to do with it, it was all based on color.
A childhood belief about weeing and pooing

others believed things like this
- When I was younger, I used to think that people with different colored skin had different color poops.— Samuel
- i used to believe that everyone had different colored pee. mine just happened to be yellow.— rick
- I used to think that little people in my penis had crayons and colored my pee yellow.— Ryan
- I used to believe that training wheels were the different colored beads on the spokes.— Samantha
- I used to believe that the people who "colored" The Simpsons ran out of skin-toned crayons.Anon
- I used to believe all liquids were water-based with things added to it to make different kinds of liquids.Anon