Uhg this. Recently decided to pick up some of my old favorites (Quake Live, Counter-Strike) and didn't realize fully what I was doing until my two daughters, ages 6 and 8 were peering over my shoulder watching me throw grenades, shoot rockets and snipe opponents (complete with blood effects).
Honestly, I don't think they even blinked, as they are exposed to a lot of media these days, but it certainly gave me pause, and started my quest for more appropriate games (for them).
To contrast this, I have several nephews of varying ages and they would do backflips at the chance to play one of these extremely violent games. Not sure what that means, or says but a man with daughters lives a different life than a man with sons. Not that my daughters don't enjoy shooting rockets and blowing up bad guys, but it doesn't have that same "power" over them as it does with young boys (which I've witnessed first hand as a boy myself and uncle)