Decisions and dilemmas

I few girls just came into the library. I know them, I've seen them at youth group, around town, and at the homecoming game. They all dress the same- skinny jeans, furry boots, and high, cement-sprayed hair. They asked me if I could find some books on witchcraft for them. Like, not fiction, but the real thing. It makes me really sad for these girls- they don't know what they're getting into. But I can't stop them from looking or refuse to help them find what they want. That's my job, after all. I'm supposed to help people find their books, without asking questions. But do I speak up? Do I say something? I guess I don't really care what they think.... but as their friend (okay, maybe not friend), as their peer, their fellow youth group attender- should I take it upon myself to say something, or do I just assume they know the dangers upon which they're meddling and let them go about their business? It's hard to know what to do. Jesus, give me wisdom.