Gee, there are some good websites that have the "how to talk to your child about" topics. I do think you are on the right track to start at 8, with simplified concepts that a child can understand. You might try googling "how to talk to child about sex" and see what comes up.
well, i guess that's too early to tell for that age right?
There are books you can get that explain the basic facts of life for kids in the 5-10 age range. Hre's one that gets good reviews:-
http://www.amazon.com/Where-Did-Come-Peter-Mayle/dp/0818402539/ref=sr_1_10?s=books&ie=UTF8&qid=1282148727&sr=1-10
I definitely do not agree with you, Myketasin. The more you mystify reproduction and sex, that more likely the kids are to become overly fascinated with it and develop unhealthy attitudes (I should know!)