How do you go about dealing with the adult nature of the beginning of the Parsha Pinchas to kids aged 12 or 13?
Any on-line material you suggest, suitable for kids this young, on that part of the parsha?
Many kids aged 12/13 have already heard about sex and very often have been told specific things about sex. The information they receive could be true, false, true but expressed in a non-ideal way, etc. etc. The point being that kids talk about this stuff and they will hear about sexuality sooner than a lot of people would expect.
That being said, my Rabbi told me once that explaining to a child the concepts of sexuality within the context of learning first of all allows you to form the concept for him. This is much better than a reactionary after the fact explanation once the child has already heard idea's from other sources. Additionally, explaining sexuality to a child through the Torah allows for the idea that sex has a place within the mitzvos/Torah.
Of course you need to know the child and understand how to teach the child these topics, but isn't that true with the education of a child for everything?
I'll end off with a question that, I believe, drives home the point: What better way is there to teach a child about sexuality than through and in the context of the parts of the Torah that talk about them?