The agency says 10 children had received liver transplants but none had died.
Findings suggest the rise in cases in children may be linked to a common cold virus known as an adenovirus, the UKHSA says, adding the agency was also investigating other possible infections, including COVID-19 or an environmental cause.
The increase in infections comes after the European Centre for Disease Prevention and Control reported about 190 unexplained cases of severe hepatitis in children around the world.
The outbreak was first reported this month in Britain, mostly in children under 10, and has been since identified in at least 12 countries worldwide.
According to the World Health Organisation, 17 children have needed liver transplants as a result of the recent cases, and one has died.
Symptoms of hepatitis include dark urine, jaundice, fatigue, fever, loss of appetite, nausea, vomiting, abdominal pain, light-coloured stools and joint pain.
There is no specific treatment to cure hepatitis but drugs can help reduce inflammation and other symptoms.
