5-year-old shoots his 2-year-old sister

That's just sick. I hope people aren't just going to focus on Call of Duty even if I agree that video games tend to focus a lot on violence these days; the issue is about the harm your child could do if you give them an item that can be used as a weapon and leave it unattended particularly when the boy in this case already has a history of flareups of aggressive behaviour.