Mum, son dead after Beenleigh unit fire

The mother of a three-year-old boy who died when a fire tore through their Queensland unit has also passed away.

Crystal Cartledge died on Tuesday afternoon, almost two days after the blaze engulfed her family's double-storey Beenleigh unit late on Sunday night.

The 30-year-old had been fighting for her life in the Royal Brisbane and Women's Hospital after suffering burns to 90 per cent of her body.

Despite the efforts of neighbours to help, Crystal's three-year-old son Baileigh was pronounced dead at the scene.

The boy's father, one-year-old sister and five-year-old brother were admitted to hospital.

"I'm devastated," Crystal's younger sister Jemma Hosking told the Seven Network.

"She was a fun, bubbly, happy-go-lucky young lady."

Ms Hosking said Baileigh was a vivacious little boy, while another sister, Karlyn Hosking, remembers Crystal as a dedicated and loving mother.

An appeal established by the Logan House Fire Support Network after Baileigh's death has raised $11,000 for a funeral service.

It is understood an anonymous donor from Mount Nebo donated $10,000 of that sum.

Network spokesman Louie Naumovski said the figure must now edge closer to $20,000 to also cover Crystal's ceremony, as well as mounting medical costs.

Mr Naumovski said the family and wider community were grieving.

"We always put the fire safety message out there ... but we can't get a life back," he told AAP.

There have reportedly been 25 house fires in Logan this year.

Investigations into the cause of the latest blaze are continuing.

It is understood police are not ruling out the fire being deliberately lit.