Of all the things parents worry about happening to their children, strokes usually aren't one of them.

That's why Christina Lovett of Mattoon, Ill., and the family pediatrician thought her 10-year-old son, Josh, had the flu when he was vomiting and complaining of a severe headache in late January.

Five days later, Josh was having trouble walking. Brain scans revealed a series of strokes.

"I'm thinking all this time 'it's a virus,'" Lovett said last week in the therapy gym at St. Louis Children's Hospital, where Josh is recovering. "I thought (strokes) were just in adults."

Advanced age is still the most common risk factor for stroke, which occurs when the brain doesn't get enough oxygen because a blood vessel is blocked or ruptured. But doctors here and elsewhere report seeing younger stroke patients.

The average age of stroke patients -- 68 -- declined by three years between 1995 and 2005.

More than 7 per cent of all first-time stroke patients are now younger than 45, according to data presented last week at the International Stroke Conference in San Antonio, Texas.

The rate of strokes among people in their 20s, 30s and 40s has nearly doubled in recent years. The exact cause of the increase is unknown, but doctors speculate that rises in obesity, diabetes and high blood pressure could be to blame.

"This is just the beginning of this alarming trend," said Dr. Jin Moo Lee, director of the stroke section of neurology at Washington University.

"Normally it takes on the order of decades for diabetes to wreak havoc on the blood vessels."

There isn't any evidence of a similar increase in pediatric strokes, which are rare and usually have different causes, such as congenital heart defects or drug reactions.

About 9,000 children have strokes each year, according to the pediatric stroke program at Children's Hospital of Philadelphia.

"Strokes in the pediatric population are as common as pediatric brain tumours," said Dr. Michael Noetzel, chief neurologist at St. Louis Children's Hospital.

Warning signs of a stroke can include loss of balance, severe headache, difficulty with speech, vision problems, dizziness and sudden weakness or numbness in the face, arms or legs, usually on one side of the body.

Because strokes have not commonly been considered a pediatric issue, and the symptoms can mimic other disorders such as seizures, there are often delays in diagnosis and treatment.

Children also have a more difficult time describing their symptoms, which can be subtle.

Kids like Josh Lovett bounce back from strokes more quickly and fully than adults, said Noetzel.

On the other hand, it's difficult to tell in a 10-year-old the skills such as problem-solving and organization that may be compromised in adulthood.

Children "are in some ways more vulnerable to long-term issues," said Noetzel.