Video games and violent behaviour

I recently had a seven year old tell me his mum lets him play “Call of Duty” which is a first person shooter game, with a certificate of 18. This left me battling with the tired old question, whether video games encourage violent behaviour in children. I have known him all his life and other than his usual hyperactivity, there seems to be no significant change in his behaviour, however no one knows how this will affect him in the future. I am looking to write an article on this topic, so let me know how you feel about letting your child play with such games. 

useful free link on:  A parent’s guide to video games, parent controls and online safety