“We’ll always keep you in our heart,” one wrote. “Rest in peace beautiful angel.”
Another said: “Our lives and our hearts won’t be the same anymore.”
Mary Akoom told Nine News her son and Isaiah used to play together and she was in disbelief after the tragedy.
“He was a very happy boy … very wise. I miss him so much.”
Kevin Georgiadis, 52, tried to help the boy, telling The Age on Saturday he heard screaming outside the building just after midday and rushed outside to find a woman carrying a newborn, telling a crowd of onlookers that another boy was still inside her flat.
“She said, ‘the baby’s up there’… I thought, ‘how come no one’s going up?’ It didn’t look that bad,” he said.
“When I got in there it was just black. As soon as I got in there, [the fire] started to pop off … I went in as far as the kitchen and the lounge room. I couldn’t go any further.”
Mr Georgiadis, who suffers from emphysema, said he then ran back downstairs because he was struggling with smoke inhalation and told firefighters he believed there was another child in the apartment.
He told Nine News on Sunday that Isaiah was a “beautiful boy”.
Part of the low-rise public housing building, at the corner of Nicholson Street and Clauscen Street, remained cordoned off on Sunday.
More than 35 firefighters brought the fire under control within 20 minutes. The cause of the fire is not yet known. Police are investigating.
Firefighters were on scene four minutes after the alarm was raised. They also rescued a man from an upper-storey window ledge, who was calling for help as firefighters searched the rest of the building for trapped residents.
The man was brought down to ground level using a nine-metre ladder. No one else was injured.
A 25-year-old was also treated for smoke inhalation.
Witnesses drawn to the scene by the wailing sirens and thick smoke had their personal details taken for contact tracing purposes before they were asked to disperse.
with Paul Sakkal
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Simone is a crime reporter for The Age. Most recently she covered breaking news for The Age, and before that for The Australian in Melbourne.