And Harry, 4, and Archie, 18 months, will no doubt need that sibling strength for a lifetime of infusion treatments ahead of them.

Harry and Archie have atypical haemolytic uraemic syndrome (aHUS), which is characterised by the formation of clots in small blood vessels, leading to kidney damage and other organ dysfunction.

The boys get treatment at the Royal Children’s Hospital, and have infusion-based therapies to stabilise their blood, every eight weeks, in regional Victoria.

Their clinician, Dr Tom Forbes, said: “Harry and Archie will need to do the infusions for the rest of their lives. Patients with this condition can progress towards severe kidney disease and failure.”

Mum Lisa said the boy’s health woes came out of nowhere. She said Harry was five months old when he suddenly appeared really sick, lethargic and pale.

She took him to a hospital near their home in the state’s northeast where doctors decided Harry should be flown to the RCH for urgent care. He spent six weeks there for treatment.

“They thought it was a blood condition, but they soon crossed that off the list and moved us to nephrology (pediatric medicine related to kidneys).”

Archie’s health issues were apparent at five weeks of age.

“He was very lethargic. I knew something was wrong because he was never an easy baby to get to sleep. The next morning he was visibly yellow.”

She rushed him to hospital. “Archie was lifeless,” Lisa said. “They put him on oxygen and got some blood into him.”

He was also flown to the RCH for immediate care. After Harry and Archie were diagnosed with aHUS, the brothers needed infusions every two weeks, and later, every four weeks.

Their sister, Isabella, 6, does not have aHUS.

Lisa is thankful for the treatments and especially grateful they now take place at a clinic close to home.

“We’re on a lifelong journey of managing their health,” Lisa said. “You look at the boys and think that they’re healthy – and they are, because the treatment keeps them that way.”