They were moved to a hospital in the UK for the transplant.
A second child diagnosed with an unknown strain of hepatitis has had a liver transplant.
The Irish child was transferred to a hospital in the UK for the transplant.
The total number of confirmed cases in Ireland has risen from 8 to 12 in recent weeks.
One child sadly passed away and two needed liver transplants.
According to the HSE, the cause of this strain is still under investigation.
The Health Protection Surveillance Centre said 12 cases of the unknown strain are under investigation.
All patients have been under 12.
They have also all been hospitalised, the HPSC confirmed.
Parents have been told to be aware of the symptoms of hepatitis.
They have also been reassured that cases are rare, but knowing the symptoms will help detect it quickly.
The HPSC stated: "All probable cases are in children between the ages of 1 and 12 years of age and all have been hospitalised.
"Two children have received a liver transplant and there has been one death associated with this disease."
If you're concerned about your child and fear they may have it then seek medical attention immediately.
The main symptoms are jaundice, a fever, diarrhea.
Kids may also have respiratory issues.
Children also may suffer from gastrointestinal issues.
