Evolution for a 6 year old

I didn't think I'd be here this soon. I haven't boned up on my science and the origins of life on Earth enough to be confident I'm not misinforming my son.
We are raising our children Catholic, so of course they know that God created life and earth and all that, but we also believe in evolution and the big bang... it's just that God caused those events to take place.
Until now, Luc has been fine with the basics... God made us and made the Universe. After brushing his teeth tonight, Luc turned to me and asked, "Mommy, did an egg just come from outerspace and then it was there and so then there were chickens, or what?" And I ask, "do you mean, what came first, the chicken or the egg?" "Yes, did a chicken just come here and then start laying eggs or did an egg come here first?"
So, my non scienctific self started to describe how there were other animals here first and that eventually an egg was hatched that was the first chicken. Then he started asking, well, how did all those other animals come to be. I tried my best to mold some answer like life started as just a bunch of tiny, tiny animals and they changed over millions of years, becoming dinosaurs and then those animals died and then new ones evolved. He seemed to accept my answer. But now I really think I need to get to the library to find a book to describe evolution on a kindergarten level. I know for sure that I didn't have those kinds of questions until I was much, much older. I accepted the fact that God created the earth in a week and man was created on the 6th day. I didn't even question where the dinosaurs -- or chickens -- came into the equation.