There are two facets to sex ed -- teaching about the basic facts, and teaching about the deeper meaning of sex and the values that maximize the enjoyment of sex while minimizing the potential problems.
I would first address the mechanics, and I think the boy and the girl should get identical information in this respect, though there could be some difference in focus due to the obvious biological differences that could lead the boy to focus on some different issues than the girl would.
When it comes to the second facet, I think the conversation would have to be tailored to the sex of the child. The boy would have to be reminded of the responsibilities that come from sex, and the need to make sure that he is not responsible for any child ending up with a deficient upbringing due to his irresponsibility.
A girl would have to be taught about the need to look out for her own best interests in relationships with boys, and not be coaxed into unprotected sex with a boy who will dump her if she gets pregnant. She also needs to be taught about the responsibilities that come with sex, and how it is up to her to help secure the best circumstances for any children that she may have.
The analogy I would use about sex is to compare it to fire or water. When controlled and used for their proper purpose, fire and water are essential to our lives, and enhance our lives tremendously. When they are out of control and control us, and/or are used for purposes other than what they are intended for, they bring untold misery and grief.
So I guess the bottom line that I would try to teach them is -- control sex, don't let it control you, and use this gift wisely to enhance your life, and not foolishly in a way that will ruin or damage your life. I'd probably try to point out some examples that they could relate to of each.
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