Investigators are trying to piece together what caused a shed fire that killed two children and left their two siblings fighting for life.
The four Victorian children were playing in the rear shed of a Corio property, near Geelong, on Sunday morning when it caught alight.
Two of the children, three-year-old Saige McGregor and 18-month-old Ashlynn McGregor, died at the scene while their older brother and sister, aged six and four, were flown to the Royal Children's Hospital in a critical condition.
The children remained in a critical condition, a hospital spokeswoman confirmed on Monday.
The siblings were in induced comas in intensive care and had undergone surgery, with more procedures planned, Seven News reported.
A GoFundMe page organised to raise money for the children described Saige and Ashlynn as "beautiful angels" to their siblings in hospital.
"This family will never be the same without these children in their lives," page organiser Daina Leech said.
"I'm hoping to help this family ease the financial cost of laying those beautiful babies to rest as this is such an unimaginable situation for any parent to go through."
Police Inspector Emma Bartel said it was a chaotic scene when emergency services arrived and the circumstances of how the fire started were unclear, although it was not being treated as suspicious.
"There is a lot that we don't know at this stage," she told reporters.
"We have spoken to family and we have spoken to neighbours.
"We are trying to piece together the events of what has taken place."
The devastated mother wasn't yet in a position to provide further details, Insp Bartel said.
Arson detectives are investigating, with police desperate to provide answers.
The children's aunt and uncle Anthony McGregor and Sarah Guardiano remembered Saige and Ashlynn as boisterous, naughty and loving.
Ms Guardiano said the children's mother ran into the shed and pulled her two eldest children to safety, sustaining burns to her hands.
A couch inside the shed, used as a dog bed, caught alight while the children were playing.
"Pulling all those babies out, like you can imagine, you know, having to call the fire brigade having to put out a fire having to pull out your children ... she did the best she could to get them all out as quickly as she did," Ms Guardiano told reporters.
Mr McGregor said the children's mother was destroyed by the loss of her two youngest and was staying at the hospital bedside of her surviving children.
Insp Bartel said some neighbours in the close-knit community tried to assist the rescue before emergency workers arrived.
"There is a lot of this community rallying together for the sake of the families that are involved."
Insp Bartel warned it would take time for detectives to get to the bottom of the tragedy.
"It is unfortunately the worse-case scenario of what we could expect with an incident like this," she said.
Deputy Prime Minister and Corio MP Richard Marles said the loss of the children's young lives was a tragedy.
"At this time the greater Geelong community is thinking of them and the two children who are in hospital" he wrote on Facebook.
A report will be prepared for the coroner.
