You do not know how many times over the course of 15 years I have heard the phrases "I like sex," "Do you like penis?", "Do you eat vaginas?" and almost every time it's typically a boy between the ages of 10 and 15 and they come to you and expect you to react in an explosive way. I typically just laugh or ignore that silliness and the lack of response usually nullifies future behavior. But I have heard the gambit of sex talk from kids.
Take last week for example when I was at an elementary school. I visit this school once every other week and have a pretty good relationship with the kids. In the toilet I was approached by two boys and one comes up to me and just say "Penis". Then he says, "Do you have a penis?" I had just taught them the phrase "Do you have ~~?" And "How many ~ do you have?" So I was thrilled he was using the phrases correctly. This time I pretended to misunderstand his English and replied "No I'm sorry I don't have any pretzels." To this both boys laughed and ran off thinking I didn't have a penis.
But I have had kids ask me if I like vaginas, how many girlfriends I have done it with, do I like boobies (they say opai in Japanese) or if I like anuses. I have really heard all sorts of weird and strange stuff and I just chalk it up to kids being curious, hormone changes and the lack of proper sexual education in Japanese schools. Sex is a taboo subject and by making it taboo you get kids that are directed to use those words. Their regular teachers never talk to them about these subjects and kids often view the foreign teacher as a person they trust and can chit chat with due to the rarity of time that I get a chance to see them.