How do little kids know is bad, with even knowing what it is?

i never "knew it was a wrong thing" because it is not wrong. i knew it was something that made people uncomfortable to talk about. but i guarantee you if you try to explain what is to a kid and dont say anything about it being "wrong" they will be perfectly willing to talk about it in public. we are not born with the thought that things like that are taboo, that is instilled in us by the society around us.