My hubby has one of the Call of Duty games for his PS3. My kids sit and watch him play. However, the only way I would let my child play a shooter game like Call of Duty, is if they can explain to me what is wrong and right about real gun safety. I want to know that my child knows and realizes the difference between a game and real life. They do have a children's cartoon game for the wii where they shoot cartoon aliens.
Right now at ages 7 and 9, both of my kids have had a little firearms safety training. My older brother and younger sister are both army soldiers and they have taken me and my two kids out shooting on a gun range. Before anyone started shooting, my sister made it a point to sit my kids down and talk to them about when it is appropriate to handle a gun.