Another 11 children have been struck with hepatitis, with one needing a liver transplant as a result - but experts have moved to reassure parents that the Covid vaccine is not to blame.
UK health officials said more than 250 cases of hepatitis have now been identified, although the rate is slowing.
The surge in worldwide cases in recent months had left medics scrambling for answers, but an update this week on the investigation suggested that they are connected to adenovirus.
Since the last update just over a week ago, one more child has needed a liver transplant, bringing the total number to 12.
There is no evidence of any link to the coronavirus vaccine, experts said. The majority of cases are in under-fives who are too young to have received the jab.
Friday's update said the investigation into the cases suggests they are connected to adenovirus, but the probe continues.
Adenoviruses spread through coughs and sneezes and cause illnesses and symptoms such as colds, sore throat and bladder infections.
Of the 251 confirmed cases, 180 are in England, 32 are in Scotland, 17 are in Wales and 22 are in Northern Ireland.
The cases are mainly in under-fives who initially go down with diarrhoea which is followed by the onset of jaundice.
No child in the UK has died from the disease.
Dr Alicia Demirjian, incident director at UKHSA, said: “We are continuing to investigate what may be behind the increase in hepatitis but recent findings continue to indicate that adenovirus infection is playing a role.
“It’s important to remember that it’s very rare for a child to develop hepatitis so parents should not be unduly concerned.
“Maintaining normal hygiene measures, including making sure children regularly wash their hands properly is good practice all year round. It helps to reduce the spread of many common infections, including adenovirus.
“We continue to remind everyone to be alert to the signs of hepatitis – particularly jaundice, look for a yellow tinge in the whites of the eyes – and contact your doctor if you are concerned.”
