There is a really disturbing movie called "Kids" that deals with this scenario. It's about 10 years old.
It's shocking, probably should be X-rated, and is very brutal.
Basically, it follows some pre-teens in an almost documentary fashion, including one predatory boy who has AIDS and does not care.
It is VERY explicit, but I recommend parents screen it and consider showing it to their children --- I believe it may scare "kids" into avoiding this fast life.
I remember seeing the movie several years ago. To tell you the truth, I think it does have an NC-17 rating (the "X" rating is a thing of the past). However, to the best of my recollection, the kids aren't pre-teen. I think they are more like 16-17.
I just mentioned the movie "Thirteen" and it is another very shocking and disturbing movie.
I think it's good to know what other kids may be going through, and to keep your own kids away from them.