Alright, here's the scoop of a woman, a gamer, and someone who is thinking of having kids.
At a young age (from 1-10) many kds are subject to the "monkey see monkey do" theory. I hate to say it, but kids may try to emulate violence they see. Even good parenting can't stop the kids from doing or SAYING something they've seen in a violent video games.
I've seen and heard stories of kids saying and doing things they've seen in movies and it's interesting to say the least.
Would I let my YOUNG child play violent games? Most likely, if it is a fighting game like Street Fighter, then yes. If it is a chainsawing, swear every 3 seconds game like Gears of War, than no.
It all comes down to judgement on a parents part. A game like Halo3, even though it has an M rating, would be ok in my eyes for a kid to play. I game like Modern Warfare 2, I might have to think twice about.
Oh and about argument of "games not being based in reality". Have you seen games lately? Games have changed graphically so much in just 10 years. The games I played were not nearly as impressive as games today. Some games are so lifelike that it would be hard to tell the difference. The "games not being based in reality" argument is weak anyways. When I was young, I knew power rangers wasn't real, but that didn't stop me from trying to be a power ranger. You can tell a kid "it's just make believe" but kids will still try to emulate what they see. One of the daycare kids tried being a dinosaur because he watched "The Land Before Time", clearly not based in reality, but the kid ran around trying to be a T-Rex anyways.
I'm honestly both surprised and a little taken back at how hypocritical some are. If a story about a 10 year old who only plays violent games comes up, you blame the parents for not controlling the child, yet you yourselves believe that letting your child play would be ok.
Be a good parent, when your kids are young, play the game or at least educate yourself on it. Too often parents buy M rated games for young kids then wonder why they hit or curse.
Always Always Always educate yourself.