Read the CNN article "Why Young Christians Aren't Waiting Anymore" by John Blake and say what you think should a Christian parent should do.
The end of this article suggests two things that parents should do.
First, there is the suggestion that people in Biblical times married much sooner and therefore did not have to wait as long to have sex. This would imply that one thing that Christian parents could do would be to stop trying to promote abstinence until marriage. Such parents could emphasize waiting for the right person or waiting until you are truly in love, but would not be so dogmatic about waiting until marriage.
Of course, this would not be acceptable to many Christian parents or youth pastors. In that case, we should look to the other thing that we see in the article--the idea that youths today are bombarded with sexual messages and the "do what feels good philosophy." Christian parents who cannot accept the idea of premarital sex should try to limit their kids' exposure to these messages as much as possible and should try to present them with a philosophy of life that is based more around doing what is right than what feels good. This may not work, but it seems like the only real alternative to giving up.