Alee,
I'm so glad that your Pediatrician is a resource! That is wonderful. Glad your inlaws are supportive also. The testing will give you lots of insight and I'm very pleased for you. I think our children need us to "mirror" back to them their nature, which includes lots of things, but the "shape of their mind" is certianly one of them.
If it's any help, I called "DNA" a "map" that gives directions on how to build a baby. I said that Daddy's DNA and Mom's DNA are helped to be put together by God. I tried to make jokes about it. I found that my son was particularly interested in the "what does birth feel like" and that I was comfortable pointing out where his DNA will get packaged up someday, and where it will come out, but that it isn't the same tube as the pee. The female anatomy was left more shadow-y. I think I probably made reference to the way his lego and k'nex pieces fit together, when he finally got around to asking.
I think that we can explain a lot if we look at if from their point of view, use words and actions they are familiar with, and stick to the spirit of the explaination.
Smiles,
Trinity
