Society's changing and kids hear about it from everywhere except the home. It's a sad thing because, everyone's quick to discuss the pleasures and every contraceptive imaginable, but not many discuss the emotional aspect of it and the impact early sexual activity has in the long run.
Children shouldn't be taught with the mindset the they're going to have sex anyway and I'm not saying that they should be shown STD pictures or told that sex is a bad thing, but when kids aren't mature enough for sex. Ultimately most of sexual education should come from the home, but parents have to take the right approach.
Early sexual activity makes it very difficult to sustain relationships. I know being a guy, I always wanted to respect my female friends, but it was difficult to sustain those friendships without thinking about sex. Another thing is we're in an ever changing society, sexting wasn't possible at one time. Pornography is easily accessible through computers, phones, and other devices, so kids can be exposed to it very easily.