DENVER -- Hospitals across the metro area are reporting an increase in cases of childhood respiratory illnesses. In fact, pediatric units at some hospitals are completely full.

"Currently the ER is seeing about 200 kids a day on average," said Dr. Erika Sidney at Children’s Hospital in Aurora.

On the other side of town, at Sky Ridge Medical Center, all 14 in-patient beds in the pediatric care unit are full, as well.

"Every child is picking this up," said Dr. David Stocker at Sky Ridge Medical Center.

Doctors tell 7NEWS most of the cases are RSV, respiratory syncytial virus. It’s a viral infection that causes inflammation of the airways. They’re also seeing cases of pediatric pneumonia, a bacterial infection. Both illnesses can make it difficult to breathe.

"The younger the kid, the smaller the kid, the smaller the airways and the harder work they have to do to get the air through," said Sidney.

"If there’s breathing problems, that’s a big deal. That’s what we worry about most in kids," Stocker added.

"I was noticing a little shortness of breath and her chest moving in a way I wasn’t used to seeing," said Colleen Carlson. Her 3-yr-old daughter, Tess, has been in the hospital since Monday.

"She had the pneumonia and bacteria in her blood," said Carlson.

It’s an example of how serious these cases can be.

So how do you know if your child has a bad cold or something more serious?

"If they’re breathing very quickly, or having a hard time breathing, or they are breathing so quickly they can’t feed, or they’re having a hard time talking, that becomes a big deal. That’s something we definitely need to see right away. You don’t want to wait around," said Stocker.

Carlson said she noticed the symptoms, but also followed her gut instincts.

"I was glad I listened to my gut and went for it, and saw the pediatrician and got that chest x-ray. We know we’re getting the best care now. But it was very scary, very scary," she said. According to doctors, children 2 years old and younger are most at risk.

Doctors said you can expect to see more of these illnesses for the next month, before they start to decline. Your best protection is good hygiene. Doctors also told 7NEWS good hydration can help prevent the illness from becoming more serious.