Children may have periodic limb movement disorder or restless leg syndrome. Some children have narcolepsy, uncontrollable daytime sleepiness, which researchers suspect stems from a problem in the hypothalamus related to a hormone that is believed to control the sleep-wake cycle.

Teenagers have a unique challenge, called delayed sleep phase. They're night owls. "If the world revolved around them, they'd go to bed at 2 a.m. and get up at 11, then go to school at noon. Unfortunately, that's not the way the world works. But at some point in preadolescence, there's a push in the circadian clock to move later into the night. Even if they go to bed when they're asked to, they sit there until 2 a.m. and don't sleep," Gault says.

Treatment may involve light therapy combined with other things to overcome it, he says.

Light is, in fact, the most useful tool to set the body's internal clock, he adds.

---

E-mail: lois@desnews.com