(CBS) — Kidney stones: not something you’d expects in kids.

But more and more of them are ending up in emergency rooms.  So what’s causing this drastic increase? CBS 2′s Mary Kay Kleist explains.

“It felt like I was getting stabbed in the side, and it hurt really, really bad,” 13-year-old Michael Wiggins says of the kidney stone he had two years ago.

Madison Ryan had three kidney stone episodes. She’s 15 now.

“The big increase is in the young adolescent population. So from age 10 to 16, is where the big increase we’re seeing in stones,” Craig B. Langman, professor of pediatrics at the Feinberg School of Medicine, says.

Kidney stones can form when highly concentrated amounts of calcium, magnesium and phosphorous build up in the urine. One factor is genetics.

“My dad has had one, his older brother had one, and my great-grandma had some,” Madison says.

Dietary influences are also to blame, Langman says.

He says higher obesity rates and too little calcium are also often the culprits.

“If it’s a calcium-based stone, which most stones are in kids, I should be drinking less calcium, right? The answer is no it’s just the opposite. We know that the more normal your calcium intake, the less likely you are to have a stone,” he says.

A fourth explanation for kidney stones in kids: diets that contain too much sodium.

Kendall Oslowski’s mom, Mindy, helps her monitor her sodium intake. Kendall had three episodes of kidney stones in three years.

“Children who make one kidney stone tend to make additional kidney stones,” says her doctor, Richard Kaplan, director of pediatric nephrology at Advocate Children’s Hospital North.

Dr. Kaplan suggested some dietary changes.

“She’s really drinking a lot more fluids. And she’s been working really hard to eliminate the salt in her diet,” he says.

Mindy Oslowski said Kendall uses a phone app to track her salt intake.

Restricting salt is hard, especially for kids. One hot dog has 670 mg of sodium, almost half of her daily allowance.