I am a dad and have three sons. My eldest is nine and wants to grow up. He is constantly pushing at his boundaries, regardless of what they are. One of those is the age rating of the games and films he is allowed to experience.
The latest one he wants to experience is Total War: Shogun 2. I haven't played it through yet - but I have played Medieval. It will be interesting to see how the improvements to the engine have impacted it's suitability for children. I am yet to decide whether he can. Until that point - it's a "No" - but he knows it's being considered.
My children know that they can ask anything and discuss everything with me and get a fair hearing. I know that biologically their ability to assess risk is not fully developed until their early twenties. I'm there to try and help them do that. I spend time looking and listening to the games. Some, like Skyrim, I allow them to watch and play supervised. They love exploring the land - but I can steer them clear of vampire caves and encounters with demons of murder. Others, like Dawn of War, feature a lot of violence - but mostly clean language, tiny character models mostly played at a distance and it's all fantastical.
Some games have simple tools that make my life much easier. Brutal Legend, for example, pauses the introduction video at key locations and asks whether I want to block profanity - and later it asks if I want to show gore. Once I've chosen - the game content is modified and I am much happier to let him play. This kind of tempering mechanic is rare in a game and a real delight when I find it. I would love for more developers to introduce this kind of thing.
Most games don't give me a choice and the rating system is inadequately detailed. However a simple decision is about online chat/talk with random players around the world. I am much more concerned about trash talk and bullying which I cannot police than I am about cartoon violence. I would imagine that more people have suffered from sledging, jibes and harassment, to the point of suicide, than have been inspired to commit violence themselves.
Perhaps the danger of violent shooters is reflected more by the invective aimed at others, and the "couldn't care less" attitude towards other people's feelings than it is in episodes of actual physical violence. Like the road rage we all experience from time to time. We're safe in our bubbles and vent anger, probably disproportionate, ignorant of the target of our ire. In a car the other person seldom sees us and doesn't hear us. On the game mic, however, or in chat - it's a personal attack. In any case - I don't want my children opened to that before they are older and more self-assured - and I don't believe in parenting by throwing them in the deep end and shouting at them to swim or drown.
Graphical fidelity and realistic physics and developments in sound effects make modern games a significantly different experience to top-down 2D sprite killing of GTA - or the pixellated 'collide with the scenery' wooden acting of Resident Evil (scary as it was). As much as I admire the visceral thrill of modern first-person shooters - the swearing, level of perceived threat and violence is very affecting. My instinct is to keep my children away from them and I think it's a good choice. It's a very different medium now compared to when I was young and so my assessment of whether I would be happy with my kids playing any game has had to change now I'm in charge.
Children are very sensitive. They are affected by violent action games and films. You can see their behaviour change after playing or watching one. It's probably short-term and can be turned into a learning experience. However I have also seen the effects of online bullying - and a single incident affects kids for days - even weeks. That's what I'm most aware of and I will work hard for them to manage their exposure to risk and build their self-esteem and communication skills to interact with the online world.
Much of which is openly and sneeringly hostile to innocence.