"But until now," she added, "there has not been a sound epidemiologic study to confirm or refute suspicions."

Dwyer and her colleagues report their findings in the Journal of Urology.

Kidney stones develop when the urine contains more crystal-forming substances -- like calcium, uric acid and a compound called oxalate -- than can be diluted by the available fluid.

Small stones usually pass through the urine without any special treatment, though kids may need pain medication and plenty of fluids to help the stones along.

Large stones that block the urinary tract, however, may require hospital treatment.

It's not always clear why some kids are "stone formers." There might be lifestyle factors, like getting too little fluid and too much salt. And some researchers have suspected that the rising obesity rate might be leading to a higher incidence of kidney stones in adults and kids alike.

For the current study, Dwyer's team combed through a database with medical records from all healthcare providers in Olmstead County, Minnesota. They focused on the 25 years between 1984 and 2008.