When I was little (now i'm 19) there was a milk commercial on TV where village family went in field and then boy started milking cow by... pumping her with her tail like pumping water with handle, and mother was gathering milk pouring from udders. For some time, I believed this is actually how we get milk from cows! (my mum iluminated me when I told her my theory once...)
A childhood belief about adverts

others believed things like this
- 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
- When we were little my sister thought if you mixed cow’s milk and water you’d get goat’s milkAnon
- I used to believe that milk came from cows, so water came from horses. hahah— Melissa O'Connor