Having done some safeguarding training recently, exposing children to unsuitable (over age) material is a safeguarding issue that 'would' be follows up (obviously not all guns blazing... It's real life after all... ;-) ).
But folks.... The worst thing children get exposed to. Is apparently online porn (oh and sharing things via web cams etc). And according to research (saw a documentary and there are stats but frankly I am not going to google them, I will just have to wade through course notes), this IS far more harmful to their well being and view of women etc, than any game. There was an article in a newspaper (guardian I think), that said children admitted to not knowing where they stood. dH himself went through a porn phase, and said he stopped 'because' he realised it was altering his expectations I realistically. There is little evidence to suggest the same is true of violent games, no matter how abhorrent they are.
The only issue for very young children is that their sense of reality etc can be blurred (so might disclose something that actually happened in a game for example), the older they get the less this is true, but there is a small danger of normalising unwanted behaviour when exposed too young (which is why there is an age restriction. Doh).
But like I say... Children are exposed to far far worse, and again, parents are not aware. Most shocking was learning that older junior age children have been know to sext etc.... In my opinion this is a more worrying issue than a made up game, because folks, it 'is' real life.
That said, no amount of begging will get me to buy them as I hate 'scary' games!