One of the oldest stereotypes about kids and videogames is that videogames have an unhealthy effect on young minds - that it makes them more prone to violence, less able to pay attention, and generally turns them into assholes. Of course, none of this has any actual evidence - it was just the typical reaction that pops up when a new form of entertainment emerges that kids "get" and adults don't.
In reality, videogames have a lot of positive effects - from encouraging teamwork, creativity, and honing hand-eye coordination. But mostly, they're just fun as heck to play. So just chill out a little, okay?