MapleStory might be fun, but that is more in the 10+ category. There is far less immaturity compared to it's past. RuneScape is an all ages game for the most part though it isn't free for the full experience. There is always Cars Online and POTCO but they aren't the funnest. Of course if you mean offline, there is pretty much the entire Nintendo lineup. And those are great games at all ages. I'd suggest Animal Crossing, New Super Mario Bros or any Mario game from the main series, Super Smash Bros Brawl (Rated T for comic mischief and cartoon violence but it is fine for 8 year olds and is a amazing game to play together), and The Legend of Zelda series (particularly Ocarina of Time for N64, Virtual console, and Gamecube as well as Wind Waker and it's DS counterparts Phantom Hourglass and Spirit Tracks).
LOL You really need to be specific.