Genre: Tower Defense
Zombies can be quite violent, but so can plants. Plants vs. Zombies pits a variety of adorable plants against the undead in a mission to protect a farm. Sure it sounds a bit crazy but give it a play and see why Plants vs. Zombies had to be ported from its mobile version. You just can't front on a game that became so popular that it's being used to get kids to brush their teeth.
By the way, you can get Plants vs. Zombies for free right here (Until November 11, 2012).