Re: RPGs for Dummies: Getting 5 - 8 year olds into the hobby
I once taught a group of 12 year-olds 3.5 D&D, so I feel strongly that if they want to play, they'll learn with a good teacher darn near any system.
That said, Numenera, with its Cypher System, I believe to be good for kids. The rules are very simple, and there's great room for the GM to adjudicate. As the point of the game is to explore (you actually don't gain XP for killing monsters, but for discovering things), it encourages kids to think of other solutions than just killing monsters and taking their stuff (though you can do that too). A friend of mine has a 9 year-old daughter, who, along with her 5 year-old brother, plays Numenera with their dad as the GM.
The nice thing about it is because the rules are so simple, you can easily make up monsters or NPCs to your players' comfort level. Some Numenera monsters are quite disturbing, but you can re-skin them effortlessly, or just make your own with the game mechanics.