Teaching the difference between fact and fiction?

A discussion came up about a book in my school that I teach in, The Chronicles of Vladimir. There are a few scenes (or rather sentences) that are definitely grotesque. It was called to attention because a faculty member thought this wasn't appropriate because of a situation, and maybe she's right. (The thought of banning or judging books always makes me cringe) and the faculty member is just looking out for the student. No problems there but I did some looking around and The Hunger Games has come up a few times because of the berry scene at the end of the book which implies suicide. And then an uneducated reader said that the English teachers (being me) should only teach the classics where all things literary are clean!

*UPCOMING RANT*

UM HELLO! I am pretty sure George kills Lennie, and Piggy is killed by everyone, Hester is ostracized, Tom is shot 17 times right before he makes it over the fence, and the family in The Pearl! Yes, classic literature is very clean. HA!

But I think the bigger issue is how do you teach a child that fiction is exactly that, FICTION? What if they can't see the difference? How would you approach this?