Emergency services were called to Newbury Street, Werribee in Melbourne's southwest, just after midnight on Monday.
Crews extinguished the blaze before finding a child deceased inside while a male resident was taken to hospital with serious injuries, Victoria Police said.
The child has been identified as three-year-old Jordan Dashwood in multiple media reports and a GoFundMe launched by a family friend.
"Little Jordan was a bright light in this world, full of innocent joy, and his absence leaves a void that can never be filled," the organiser, Jardine Jackson, wrote.
Jordan's mother Janelle and his older brother managed to escape the property, while his father Jeremy remains in a coma in hospital, she said.
The 40-year-old father-of-two suffered burns after attempting to save his son, according to multiple media reports.
Two family dogs also died at the scene.
"In a single night, this family's entire world was reduced to ashes," Ms Jackson said.
"They did not just lose their home; they lost their precious little boy, their loyal pets, their memories."
Fire crews arrived at the scene within minutes, where the single-storey brick home was fully alight, Fire Rescue Victoria said.
It took about an hour for 40 firefighters, including Country Fire Authority crews, to bring the blaze under control.
Authorities remained at the scene late Monday morning, where forensics personnel were seen studying the charred house.
The property has been cordoned off with police tape, with ash laying in a heap beneath a blackened, hollowed-out front door frame.
Donations to the fundraiser will go towards Jordan's funeral expenses, his father's medical costs and the family's basic necessities, Ms Jackson said.
"We cannot take away their pain, but we can wrap our arms around them as a community and ease the crushing financial burden of this nightmare," she said.
The circumstances surrounding the fire are being investigated but it is not being treated as suspicious, police said.
An arson chemist is set to attend the scene.
Victoria Police declined to confirm media reports that investigators would consider whether an e-scooter battery sparked the blaze.
ABC has reported firefighters were told children were trapped inside the burning house but some managed to get out.
Peer support and counselling have been made available to first responders.
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