Gaming is supposed to be educational? I guess I missed that debate when I was a kid playing Super Mario Brothers, Bomberman, Hack, Space Invaders, Super C, and Link's Awakening for about as many hours per day as I could possibly fit in. When the rest of a kid's day is spent at school or outside (I spent copious hours TRYING to get lost in a national forest next to my house), or watching the entertaining crap they call kids' TV, why would people even want to set tedious learning methods (Dora games) as a goal? Are James Paul Gee, Henry Jenkins, and David Shaffer the only people who appreciate the Montessori-like benefits of non-educational gaming?
As TheWickerPopstar mentioned, I also recommend trying NES and SNES-era games with them. Unless your kids have been playing Crysis and Gears of War, they won't mind the graphics shortcomings, and you do want them to understand the classics, right?