Check out these other articles about young children and screens.
THE TOUCH SCREEN GENERATION and a Review of this article by Larry Magid
THE CHILD, THE TABLET AND THE DEVELOPING MIND
Latest Resarch on Internet addiction in adolescents: Prevalence and risk factors
TOO MUCH OF A GOOD THING an article in Vodafone's Digital Parenting Magazine by Dr Richard Graham see page 16
Here's a brilliant website all about doing things in nature with kids. Check it out at http://www.projectwildthing.com/