How are kids affected by the use of media devices?

There have been many studies about the effects of television on children, and those studies have expanded to include the use of cell phones, mp3 players, handheld video games, and other media devices.  A recent study by the Kaiser Family Foundation shows, among other things, how much time kids spend using different media devices.  You can read more about media usage studies at <http://arstechnica.com/media/news/2010/01/obvious-report-on-increased-media-use-among-kids-is-obvious.ars>

Here are two graphs from the study that I found interesting.

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Daily amount of time, in hours and minutes, kids spend using media devices when parents set limitations on their use versus those whose parents do not set limits.

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Correlation between amount of media use and grades: