Restless leg syndrome may be linked to low levels of iron in the blood, researchers have found.
The US study of over 500 children found that a family history of the condition also increased their risk.
The researchers say restless leg syndrome can have a significant effect on a child, affecting their sleep patterns and therefore their education.
The Mayo Clinic study, published in the Annals of Neurology, also suggests the condition is often missed in children.
Children very often describe restless leg syndrome as 'creepy crawlies,' as 'ouchies' or 'owies'. One child told the researchers it felt like walking though snow.
All the children analysed in the study attended the paediatric sleep disorders programme at Mayo Clinic between Jan. 2000 and March 2004.
Thirty-two were diagnosed with restless legs syndrome.
The most common symptoms were trouble getting to sleep or staying asleep, which affected 87%.
But researchers were surprised to find that 83% of these children had low blood iron levels.
The researchers say the explanation for the link is unknown, and could be due to diet or a genetic predisposition to low iron levels.
There was also a strong link between restless legs and a family history of the condition, with 23 out of the 32 children having a close relative with restless legs.
The child's mother was three times more likely to be the parent affected with restless legs syndrome.
Dr Suresh Kotagal, head of paediatric neurology at the Mayo Clinic and lead researcher on the study, said: "Restless legs syndrome is under-diagnosed in kids.
"If you look at children with difficulty falling asleep, you'll see a fair number have restless legs.
He added: "If affects the quality of life," he says. "They wake up frequently in the night. They wake up tired. They may also be inattentive during the day."
He said the syndrome could be the explanation behind regular bouts of "growing pains" which affect some children.
He added: "Occasional growing pains are nothing to worry about, but growing pains every night may be restless legs syndrome.
"It's like the fact that somebody might snore one or two days a month, but if it happens every night, it may be something that needs medical attention."
Dr Kotagal said the syndrome could be treated with drugs which increase the levels of dopamine in the central nervous system.
But he said there was not yet sufficient evidence, that treatment with iron could help children affected by restless legs.