The CDC says more than 100 children in 25 states and territories have contracted severe cases of hepatitis.
About 90% of the children were hospitalized, 15% needed liver transplants and 5 children have died.
"Hepatitis is nothing to play around with. So that fact that it's just popping up in kids really not understanding where it's coming from, is scary,” said parent Courtney Sharp.
Hepatitis is when the liver becomes inflamed and swells. It’s caused by infections, autoimmune diseases, drugs or toxins.
"What would tip your hand to thinking that you might be dealing with liver disease, is the presence of jaundice. The yellow in the whites of your eyes,” said Mike Leonis, pediatric hepatologist at Cleveland Clinic.
Health officials think this could be linked to hepatitis cases worldwide.
The World Health Organization says nearly 230 cases in 20 countries have been detected as of May 1.
The CDC says it doesn’t know the cause, but has ruled out hepatitis viruses A, B and C, and COVID-19 infections as a cause of the outbreaks.
The CDC thinks the cases could be connected to adenovirus, which can cause common colds, bronchitis or other illnesses.
In more than half of the U.S. cases, the children did have adenovirus.
In the U.K., it’s health security agency says 72% of suspected cases were positive for adenovirus.
"I don't really know what to make of this, except that we're in the very early stages of understanding whether or not this is a problem,” said Leonis.
Additional reporting by the Associated Press.