The first symptom describes many kids: trouble falling and staying asleep. But if your child also complains of heavy-feeling legs, and has an uncontrollable urge to move them frequently during the night, he might have a condition called restless legs syndrome (RLS).
As with growing pains, which can wake kids up at night with aches in their legs (often after they've played and run a lot), RLS can wake him up with discomfort, too. But it can also make it hard for a child to settle down at night in the first place. It may take anywhere from 30 minutes to 2 hours to fall asleep. And then he'll wake up repeatedly through the night with a need to move his legs.
If you suspect RLS, ask your doctor to test your child's iron levels—about three-quarters of patients are deficient in the mineral. If your child is, he may need iron supplements. There's also anecdotal evidence that evening exercise may help. Running, skipping, jumping—that's a treatment a kid'll love!