Learning any RPG by reading the rules is difficult--but nothing compared to learning a CCG that way.
You might want to try to hook up with a group through your local game store or book store, at least long enough to learn the rules.
Kids that age can handle enough of the rules to grasp some advanced games. Another one to look into is True20, the rules system behind the Blue Rose RPG. Blue Rose is a romance type RPG, but True20 is very simple and very versatile. It'll easily handle your average fantasy monster-bashing.
I started gaming in 1980. I have all the old D&D stuff--back to before it was D&D, with Outdoor Survival and Chainmail. If you have technical questions on that old stuff, let me know.
For kids, keep the adventures short; you know their attention spans better than I do. You might want to look at the old 1E Dungeonland and Beyond the Magic Mirror, both based on Alice in Wonderland and written by Gary Gygax.