Jake Symons, 21, has been barely able to speak since being told his two children - Maddison, 20 months, and Desmond, five months - were killed in a fire that engulfed the family home on Thursday.
Family friend Mathew Chilly, 36, and a teenager who has not yet been identified, also died in the Central Queensland fire.
The devastated father posted emotional and loving tributes to his children, begging forgiveness for failing to be by their side.
"Dad's best little mate," Mr Symons wrote.
"I had so many things I wanted to show u and watch u grow. We'll have that vb and kick the footy around in the next life - won't be long."
He described his "little maddie moo" as his everything, but said it would not be long before he was by their side.
"My first love, my everything. Dad's number one," he wrote.
"Baby, I'm sorry I wasn't there my little princess rough nut. I'm sorry my big girl I wasn't there, won't be long.
"Just a bad dream I won't wake up from because it's just not real, can't believe this."
Family and friends have rallied around the grieving father, who is now staying with close relatives as they struggle to come to terms with the loss.
"Our family is shattered - Jake lived for his kids," Aunt Sally Woulfe told AAP.
"He is in a world of pain."
Mr Symons moved to the Queensland town of Emerald, about 270km west of Rockhampton, to work as an apprentice mechanic before being diagnosed with cancer.
He lost his job, and the young family struggled to make ends meet before moving into social housing.
After having a part of his stomach removed, the family said Mr Symons was undergoing specialist treatment in Brisbane and was to return home on the day of the tragedy.
"Jake has nothing left - his beautiful children are gone, and everything he owned was lost in the fire.
"That's why I started the fundraiser - they are in crisis. They have no money, no insurance, nothing."
The GoFundMe campaign had raised more than $7000 by Friday afternoon as pledges poured in from around the country.
"Maddison was full of life and laughter, always smiling and curious about the world around her," Ms Woulfe said.
"Little Desmond was a gentle, happy baby whose laughter brought light to everyone who met him. Their bond was pure love - and they were taken far too soon."
Emergency services arrived within minutes of the blaze erupting before 7am on Thursday in the Queensland town of Emerald, about 270km west of Rockhampton.
Neighbours with garden hoses valiantly tried to control the fire, and two anguished survivors who escaped with minor injuries were hospitalised.
Investigations are under way with a faulty e-scooter a possible source, Senior Sergeant Peter McFarlane confirmed.
"You can imagine, a fire fully engulfed is one thing, but learning four lives inside, lost inside, it's been quite traumatic on all emergency services," Sen Sgt McFarlane said.
"Obviously, our priority is the families and extended families of the victims, but also emergency services workers will require some support in the coming days."
Premier David Crisafulli said the loss of life was an incredible tragedy.
"It's the kind of event that rocks all communities, but particularly smaller communities," he said.
"The connections of school and sport and community groups, and emergency services personnel, the tragedy will ripple right throughout that community."
The tragedy comes weeks after an alleged arson attack killed a mother and two young boys at Gladstone on October 15.
Jordana Johnson, 36, and her 12-year-old son Jordan Norris were killed, along with his friend Chazz Mather, also aged 12.
Police said they believed the fire was deliberately lit, charging a 37-year-old Toolooa woman with three counts of murder and two counts of arson.
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