I agree you have to draw the line. Black Ops is rated the way its rated for a reason. Its violent, somewhat graphic and the language would not be appropriate. Granted its no worse than any war movie, the killing at least is in a combat scenario versus Grand Theft Auto (mentioned above). However the multiplayer is not that bad and wouldn't warp him but you can't get that without the story.
Edit: And lastly we need to keep he kids off these games, they are better than me and its not fair