Children who spend less time watching tv or playing computer games get better sleep, are slimmer, do better at school and are generally well behaved. Latest research has indicated this and parents who monitor their children's activities finds they are better behaved.
Parents who monitored what their children did also meant they are less aggressive because they aren't watching or playing games that contain a moderate amount of violence. Children who see less of this are more likely to switch off at night and a good sleep helps contain mood swings.
For more information on this check out this link: http://www.dailymail.co.uk/health/article-2593484/Children-watch-TV-slimmer-better-school.html