Or maybe the girls are not being let out to learn computers and play games.
Based on what my kids like, I’d say that as games go, the lamer the better. Any website associated with a brand of cereal or candy or TV show has games on it, most of them ridiculously simple, but my kids love them. The Wonka candy site (http://www.wonka.com/gamecentral/) is a current favorite. One thing Wonka has done is copied old arcade games like Pac-Man, and Wonka-themed them.
Don’t forget the games on Yahoo (http://games.yahoo.com/games/front) – there are a million puzzle games there.