Nine-year-old Evan Mohammed died after a fire in the family home in the early hours of last Tuesday.
His mum, Sheree McGill, 33, her boyfriend, and Evan's sister, Talia, 15, who were asleep on the ground floor, managed to escape from the burning house in Kilmarnock, but Evan and his sisters, Yasmin, four, and Nya, three, were trapped upstairs.
Ms McGill and a neighbour, Sean Murray, tried to get to the children but were beaten back by the flames and smoke.
Firefighters then battled intense heat to rescue the children from the property and they were taken to Crosshouse Hospital in Kilmarnock, where Evan died as a result of smoke inhalation.
Ms McGill said: "I would like to thank everyone who has helped and supported us at this difficult time. The firemen were incredibly brave and without them the situation could have been even worse.
"And thank you to my neighbour Sean who tried to get to the kids.
"Although Evan is with the angels now, he passed away in his sleep and suffered no pain. All the other children are well, so, once again, thank you from the bottom of my heart."
Evan's family believe the fire may have been caused by a faulty fibre-optic Christmas tree in his room. Several neighbours saw flames and smoke about 3.20am on Tuesday morning, while some reported hearing two loud bangs.
Forensic teams are still investigating the exact cause of the fire but it is not being treated as suspicious.