I think that it would be good for you to set limits on how long your kids should play video games per day. Though educational video games can teach your kids things, it is just as important that they go outside to play. Playing outside would not only help them get the exercise they need but also encourages socialization with others and the ability to development meaningful relationships and friendships.
The problem with video games is that they are simply not as socially interactive than I wish they were. When one player takes their turn, it is the next players turn. It is important that kids play games where they work together to achieve a common goal. This teaches kids the value of teamwork.
Though you mentioned that your kids are not obese, recent research shows that obesity in children is now the worst that it is ever been. Though research hasn't tied the childhood obesity epidemic to anything in particular, most people would deduce that it is because kids these days would rather spend their free time playing video games, surfing the net, or watching TV. Even schools have or are considering shortening or eliminating recess time all together in spite of recent research that states that recess helps improve the behavior of children.
Regarding whether violent video games are actually bad for kids, I think that the jury is still out on this issue. I've read research going both ways. Of course, I would prefer kids playing non-violent games over violent games, playing violent games doesn't necessarily mean that you will have violent kids.
I hope that this helps!
Mark Lakewood, CEO
Building Strong Families National Seminars
http://www.SuddenComplianceWebinars.com