The following information comes from the Kaiser Family Foundation website in a report called Children’s Media Use and Sleep Problems: Issues and Unanswered Questions.
Research shows that poor sleep causes a wide variety of problems among children. Many of the issues faced by parents and pediatricians -- from obesity to aggression to hyperactivity -- are caused or increased by inadequate sleep.
A lot of people don't know that while the body rests, the brain does not. The first system to suffer from poor sleep is the brain's ability to organize activities and pay attention. These are referred to as executive functions.