This is really embarrassingly stupid, but when I was young (really old enough to know better though!) I noticed that many older women had breasts which had begun to... sag. Since I knew some animals had their teats closer to the belly than the chest (like cows) I seriously concluded I had found one more proof of evolution, i.e. that past generations were physically more akin to animals in this one area. I wonder why-- I wasn't usually nearly so dumb!
A childhood belief about getting older

others believed things like this
- When i was really little, i thought that pharmacy was a shop where you could buy animals, like pigs and cows.Anon
- When I was young I believed that the windmills found in farmers fields were used to keep the cows cool.— Linda
- i used to believe that bras were bullet-proof vests for women.— emily
- When I was young, I used to wonder what if the animals turned into humans while the humans were away.— Kirk
- I used to believe that rocks are animals.— Lulzy
- i used to think that all animals were made in factories!— lalaaaalalalalallllalalalalalalalalalalalala