The 15-month-old girl is one of an estimated 1300 people world-wide with the congenital central hypoventilation syndrome - also known as Ondine's Curse - which can impact all of the body's autonomous functions including breathing, heart rate and the digestive tract.

Her first months were spent in hospital, at Ballarat Health Services for six days and in Monash Children's Hospital in Melbourne for a further 59 days, while doctors tried to find a diagnosis.

In Sophie's case the disorder mainly affects her breathing and she must sleep with a bipap machine, a mask which covers her face and forces her to inhale and exhale.

"Her breathing can slow to dangerous levels even if she sits down on the couch and starts to get tired," mum Amanda said. "And if she has a really big temper tantrum and gets worked up she starts to get grey/blue around the mouth because she doesn't seem to be able to multi-task in the sense that she screams but also needs to breathe."

Sophie's three brothers, even William, 3, are now alert to when their sister starts to tire and warn their parents to have her mask ready.

The risk of Sophie's breathing slowing or stopping means someone must be watching her constantly, which takes its toll on her parents.

Cruelly, CCHS also predisposes children to cancers of the nervous system including neuroblastoma and she is screened regularly for cancer. And because Sophie is so young they still don't know the full extent of how the condition will affect her into the future.

"This is the hardest thing we have ever had to do. It's heartbreaking and exhausting," Ms Stewart said.

"I have had post natal depression with each of my pregnancies so having to contend with that as well as the first few months of not knowing or understanding what's going on and knowing you can't help was tough."

Being apart from their sons, and unable to explain what was wrong with their sister, was also heart-wrenching.

"Early on we would stay in hospital during the week then go home to them on weekends," Ms Stewart said. "Initially we were not given a time frame about how long we would be at Monash. We left our then-two-year-old back home and when we realised it was looking quite long term we started bringing him with us.

"Then Benny and I alternated a few days at a time at Monash and going back to be with the older kids. Our middle son asked if Sophie wasn't coming home because she was going to die, and we didn't have a diagnosis then so we didn't know what to say to them."

When they finally got back to their Majorca home after more than two months in Melbourne they barely slept, getting up 30 to 40 times a night when alarms went off on Sophie's bipap machine or just to check on her.

The family now has a night nurse three nights a fortnight to watch over Sophie and a nanny to help with her and William.

"We need to have eyes on her at all times, to the point where it is quite common for CCHS children to have a nurse on hand all the time at school," she said.

The first sign that anything was wrong with Sophie was when doctors at BHS noticed she had low blood sugar. She was admitted to the special care nursery, then medical staff realised her oxygen levels kept dropping dangerously low.

She was put on breathing support but it kept having to be escalated until, at six days old, she was transferred to Monash Children's Hospital ICU which had the only available pediatric ICU bed.

Despite its rarity, doctors suspected Sophie had CCHS from early on but extensive testing repeatedly came back negative.

"It wasn't until Sophie, Amanda, and myself all had blood drawn and sent to Finland where they did very complicated testing and genetic screening that they found out she actually has it," Mr Stewart said.

"There are two types of CCHS. The first one covers 92 per cent of all cases and that came back negative, but they still thought that's what it could be and she came back in that 8 per cent that have the second type - she's the rarest of the rare."

She has monthly x-rays, ultrasound and urine testing and appointments with an oncologist, respiratory specialist and sleep specialist. Every three months she goes back to Monash for appointments and an overnight sleep study to watch her breathing.

That has been complicated over the past seven months with Sophie having to have a COVID test a week before admission and the whole family quarantining themselves for that week to further reduce the risk.

Sophie's specialists were forced to get special approval from the hospital's board to conduct her vital sleep testing because the unit has been closed because of the COVID risk.

During the stress of the weeks and months in hospital, the family found a refuge at Ronald McDonald House at Monash Children's Hospital where they stayed for 55 days.

"We stayed a couple of nights in a hotel, then we were linked in with a social worker at the hospital who got us a room at Ronald McDonald House and we stayed there," Mr Stewart said.

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"As the weeks and months passed we started bringing our boys in turn with us to come and spend time with their sister and us."

He said the staff, and other families staying there, became like family and understood the stress and anxiety about having a child in hospital. And they stay there now when Sophie is admitted for her regular testing.

McHappy Day, which supports the Ronald McDonald House charities, is on November 14, which coincidentally is also the international awareness day for CCHS.