Those games are really really addictive, my advice is not to look for such a game for your kid, those games are the most addictive games on the computer, I have played Runescape for a while aswell, luckily i found out that it is really addictive because some of my friends started buying all kind of things with real money, and started playing almost 24/7, thats when i thought, that i didnt want to end up like them, so i stopped. After a while some of my friends stopped playing aswell