I used to believe that cows just started to produce milk spointaneously at some point. It was quite a shock when I deiscovered that they are "dry" heifers until they have their first calf. Then the surplus milk the cow produces is used for human consumption. As the time from the calving increases the amount of milk produced decreases. So the cow is mated again, and after the calving she will again have a full udder
A childhood belief about general

others believed things like this
- I used to believe the Golden Calf produced liquid gold instead of milk.— Trisha
- I used to beleive that milk bottles were filled with milk, directly from the cow's udder.Anon
- I used to believe chocolate milk came from brown cows and regular milk came from black and white cowsAnon
- i used to think chocolate milk came from brown cows and normal milk came from white cows Anon
- I used to believe I could milk dogs like the cows. This was because I saw a nurse milk his cow.— Laurent and Alexis, French students in eighth grade
- I used to believe that brown cows made chocolate milk and white cows made regular milk.— andrew mient