I am happy to see all the conversation my original post started! I have to admit I will need to reread the posts. I do plan to utilize all the info:)
MON- I have to admit that I agree with a lot of what you have said. I want my boys to learn about Catholism, so they will question and have to work things out. I also, liked your thought (simplified) of explaining how god made us and we cannot understand everything.
Aquinas- thanks for your references. I will look into these. At this point, ds mostly wants to know why. Why did god choose the make things the way they are? Specifically, why man and woman? (He knows things need to be that way to have children and continue civilization.) then he asked, why didn't he make the way we have babies differently? And specific details about how long did it take...
It sounds like you could easily take the discussion into trinitarian territority, and talk about how human unity in marriage mirrors Trinitarian unity through the unitive and procreative aspects of marriage, the duality of the human nature as biological and spiritual. Personally, I would talk about how God is love, and he wanted to create a channel for his love to be expressed, and take it from there with the "sonhood/daughterhood" of humanity.
I think a lot of the answers will necessarily be "we can't know for certain", like how long it took to create Earth, Mars, etc. On that front, you could discuss the interpretation of the Genesis creation story as a story of the soul's birth, and not necessarily literal physical creation. It might dovetail nicely into a discussion of how biological evolution and spiritual creationism dovetail and aren't mutually exclusive. This link is great, as is the encyclical "Theology of the Body".
http://www.vatican.va/holy_father/j.../documents/hf_jp-ii_aud_19790912_en.htmlThese are exciting questions to think about answering!
In your place, I'd want to ensure my DS was comfortable with asking more open ended questions down the road and appreciating that our knowledge is finite. I wouldn't hesitate to link the theology to science, like evolution and the Big Bang Theory, because it's never too early to learn that science and theology answer questions on different sides of the same coin.