Just reading this thread with a lot of interest. My children are 11 and two 8 1/2.
I can't remember whether I was 28 or 29 when I lost my virginity, but my dh is the only man I have ever slept with and I am proud of it for it, it is what I wanted.
BUT with my own children if I was in your situation Maltesers I probably would be worried about the age thing, but most importantly I would be proud that my son was using contraception, and his girlfriend too, and that he/they felt that they could talk to me about it, and act in a responsible manner. The age isn't really the issue. I would want my children to start having sex when they were ready, and hopefully with someone who respects them as well, not just wants sex.
It is very difficult, but even though I had a strict upbringing, I try to be very open with mine, so that they know about life and the emotional side as well.
As for the people who are against, I suspect their children are very young, and its all very well saying, this is wrong, and that is wrong, but how could you stop two teenagers, you have to let them grow up, and all you can do is guide and support them.
Good luck Maltesers.