[TRIGGER WARNING: BDSM, ABUSE, STALKING]
You should talk to your kids about sex, of course. But this isn't about that. I've seen teen girls on Tumblr say that their friends are talking about how sexy 50 Shades of Grey is, which is very disturbing. Not because it depicts BDSM. No, this is disturbing because 50 Shades of Grey absolutely does NOT depict BDSM.
This comes direct from the BDSM community. They hate this book. They've denounced it. They've written several long pieces about how what happens in the novel is not BDSM, but plain abuse. It violates many of the tenants of BDSM, which are all based around the idea that sexual play must be safe, fully consensual, and collaborative, with equal power given to each person involved (or giving more power to the submissive partner).
According to the BDSM community, the dominating partner in 50 Shades of Grey, Mr. Grey himself, is an abusive, controlling, selfish stalker who does not care about the safety, consent or desires of the woman he's partnered himself with. The fact that many young women are looking at this dynamic and finding it sexy is not a sign of the popularity of BDSM, but a sign of rape culture. It shows that the abuse and sexual control of women is a desirable norm in our culture.
If this is what young women have been taught to find appealing, rather than a sexual relationship based on continuous, enthusiastic consent and communication, then it's no wonder so many of them end up in abusive relationships. And it's no wonder so many men consider controlling women and making them powerless to be an essential part of masculinity.
It might be hard to talk to your kids about sex, and even harder to talk to them about kinky sex, but please, for the love of god, don't let them go about thinking that abuse is sexy. Please help them get into real, safe BDSM. Encourage them to explore their desires safely rather than with Greys. Same goes with any other family members, friends, Facebook acquaintances, etc. Whenever you have the strength, please, work to counteract the idea that 50 Shades of Grey is an acceptable depiction of a sexual relationship. Thank you.