I use the Apologia Elementary Science series. I take quite a bit of ribbing about this. I do not teach my child that to be a Christian, to believe in the God of the Bible, one must believe in the Young Earth theory. I believe it is an intellectually dishonest theory. Young Earthers claim that because Christians believe God "did it," they can definitively know "how" He did it. That seems presumptuous on an huge scale. They have their theory and make all the evidence fall in line. Well, that's what the proponents of evolution do also! In our home, we observe nature and give thanks to God for it. We do not hitch our wagon to THEORIES!
Why do I use Apologia? Well, the elementary series is beautiful, and I like the scope and depth.
All this is to introduce you to, if you are not already familiar with him, Gerald Schroeder.
Now, I do not pretend to understand astro-physics or whatever it is. But the little glimpses I have had of his work intrigue me. If you are at all concerned with the dating of the planet or the universe, I would strongly encourage you to check out his work. I can not do it justice, but I will tell you it has something to do with the age of the universe in the center of the universe. He believes the Big Bang was the moment of creation. He has some formula about the expansion of the universe and the time distortion. If you divide that by the age scientists give the earth (or maybe it is the other way around) you get an age of 6 days for the center of the universe. Does that make sense? I understand it if I cross my eyes and squint! Go look him up. It is an intriguing idea....
(What I find intriguing is that a man in my husband's Sunday School class did the math IN HIS HEAD when my husband tossed out the age of the earth and the formula for time/expansion! And this man makes great huumus. Amazing!)