I was raised in the city so growing up was not exposed to many animals. When I was 6 on a cross-country trip to visit relatives with my family. My father pointed out some cows and said "Look how fat those horses are!" I believed him and continued to think cows were just fat horses for a very long time.
A childhood belief about general

others believed things like this
- When I was little I thought cows married horses, cows were all female and horses were all male. — Sheila
- I used to believe cows were ugly horses— Marlene
- I used to believe, as a child, that horses were male cows.— Martin Taylor
- I used to believe that milk came from cows, so water came from horses. hahah— Melissa O'Connor
- I used to believe that cats were the girls and dogs were the guys. Same with cows and horses.Anon
- I believed for a long time that brown cows gave chocolate milk!— Evil Mom