When I was little, I used to believe that corgis (a breed of very short-legged dogs) were made by rolling a puppy inside of a carpet so that it's legs wouldn't grow, and then let out as adults.
I also thought that boxers and rotweillers and other dogs like that were just born without a tail.
It's odd how things like that are completely normal and not a bit disturbing in a little kid's mind.
A childhood belief about cats and dogs

others believed things like this
- i thought hot dogs were made from real dogs and sum tasted good sum didnt.— Wayne
- Thanks to the movie "Annie", I thought hot dogs were made from real dogs. — Katie
- I used to believe "mixed breeds" of dogs were made by two dogs being put in a blender— Andie
- I used to believe that seals were dogs that had amputated legs.Anon
- i used to believe that dogs were furry midget who walked on for legs— doggy
- My sister and I thought cats and dogs were the same animal, the dogs were male and the cats were female.— Paul