Ezabella, aged one, was declared brain dead in a Melbourne hospital on Boxing Day and her life support switched off after she suddenly fell ill days before Christmas.

Her parents Nick Paul and Naomi Wilson, formerly of Queanbeyan, gave permission for her tiny organs to be donated to other children in need.

Ezabella was born at Canberra Hospital with part of her sixth chromosome missing which caused brain abnormalities, developmental delays and dysmorphic features.

She also had throat conditions including a tracheoesophageal fistula which caused problems swallowing, chest infections and pneumonia.

The family, including the couple's other children Joshua, 10, and Alexis, four months, moved to Melbourne from about five months ago to be closer to medical treatment.

Her aunt Hailee McArdell, who lives in Monash, said Ezabella was in good health until she started to vomit the night of December 21.

Her condition continued to deteriorate and she was struggling to breathe when doctors decided to intubate her on Tuesday night.

Soon after the procedure Ezabella's oxygen levels dropped, her heart stopped and it took medical staff 25 minutes to resuscitate her.

They cooled her body to help reduce brain swelling but a test 72 hours after the incident showed she was brain dead.

On December 27, Ezabella's parents, who are both registered organ donors, decided to donate her heart, liver and kidneys.

But doctors found her liver was damaged and her kidneys were too small.

Her heart, however, was "perfect" and could be donated, Ms McArdell said.

"That heart is now in the chest of a little boy and he's recovering well."

Ms McArdell said that was welcome news for her devastated sister, who received a letter informing her of the successful donation this week.

"She knows that her little girl's heart was beating still."

"It makes it feel like it wasn't for nothing if a little boy is living because of Ezabella's heart."

Despite her family's grief, Ms McArdell said they were "stoked" at the thought Ezabella had saved a life through organ donation.

"We would really recommend it because you never know who's going to need it.

"The family probably found out on Boxing Day their kid was going to get a heart and what better present to get at Christmas time than to hear your one-year-old is going to survive."

Ezabella's family doesn't know what caused her health to deteriorate so quickly after initial tests and a preliminary autopsy report failed to identify a cause. Her death will be investigated by the Coroner.

Ms McArdell remembered her niece was always positive and happy despite her medical conditions and treatments.

"When they were just about to intubate her she looked at all the doctors and said, 'Hi'.

"The last thing she would remember was looking at everyone and smiling."

Ms McArdell said her sister now wanted to raise awareness of rare medical conditions in the hope it will attract more research, funding and support for families.

"She just wants people to know there are other diseases and illnesses that people don't know much about."

Ezabella's loved ones will release butterflies and pink balloons on Sunday at a park in Russell where they gathered last year to celebrate her first birthday.

Mr Paul told of finding himself in the "impossible situation" of having to say goodbye to his daughter for the last time on an online fund-raising page Ms McArdell set up for the family.

"Ezabella is one year, six months and 26 days old," he wrote.

"I feel like you should all know that for a period of time that was much too short my daughter existed and she was beautiful."