I found an interesting article in the ERIC Digest on the effects of video games on children. The article gives information about how much time is spent on electronic games, the differences and similarities in gender, and effects of playing violent games. This article cited three studies on the effects of playing violent games. All agreed that playing violent games led to aggressive and negative behavior. However, another study cited stated that there is insufficient laboratory research to support strong causal statements about the effects of playing violent video games on children's aggression.
You can read more about this article at Video games research and effects.