Fire crews were called to the property in Lon Tanyrallt, Alltwen, near Pontardawe, at 01:40 BST on Wednesday.
Jac Davies was rescued from an upstairs bedroom but died at the scene.
His three-year-old brother was also rescued and taken to Swansea's Morriston Hospital along with his sister, six, an 11-month-old brother and their mother who had all managed to escape the blaze.
They were all suffering from suspected smoke inhalation which is not thought to be life-threatening.
In a tribute, his mother, Jennifer Davies, said in a statement: "My big, handsome blue-eyed boy - you're my life, my world, my everything and will never, ever forget you.
"Go ride your train up to heaven and wait for me.
"Kelsey, Riley and Andrew will always remember you."
Mid and West Wales Fire and Rescue Service said Ms Davies, called for help and neighbours tried to get in to help the stranded children.
The cause of the blaze is being investigated by the police and fire service.
Chris Margetts, senior operations manager for the fire service, described the blaze as "very severe" but said smoke detectors may have raised the alarm.
He added: "It is a very close community, and specialist teams from the fire and rescue service will be working with the community in the coming days."
Outside the family home, visibly shocked neighbours stood in the street with their hands over their mouths, trying to make sense of the tragedy.
One woman was consoled by a police officer as she laid a floral tribute at the scene along with two teddy bears.
A card left with some flowers said: "To Jack. So sad to hear you are sadly gone. Harry will miss you, seeing you smile and playing with you at school. Gone too young."
South Wales Police Det Ch Insp Esyr Jones, of Swansea and Neath Port Talbot CID, said: "I would like any witnesses or anyone involved at the scene who have not yet spoken to police to come forward with any information they may have."

Kev Brady from Gloucester said he was terrified as he paddled more than 200 miles (320 km) along the Mahaweli.
He now aims to paddle the 800 miles (1,300 km) around the coast of the island of Sri Lanka.
His previous feats include canoeing along the Mississippi and swimming the length of the River Severn.
Mr Brady said he had suffered minor scratches and scrapes during the journey, but the most "frightening" thing was having to paddle past the crocodiles.
"I was on my own and standing [on the paddle board] only 2in or 3in above the water.
"I saw a two-foot long head pop up only 5m away from me.
"These are saltwater crocodiles that can grow up to 6m long and are considered man eaters.
"I was terrified."
Mr Brady said he felt relieved to have finished the river challenge.
"I was anxious and afraid most of the day and night, in between appreciating how beautiful and amazing it was.
"So there was a lot of relief when I finished - relief I've still got both arms and both legs."
A four-year-old boy has died following a fire at a house in Neath Port Talbot.
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A paddle boarder faced man-eating crocodiles during his quest to travel from source to sea along the longest river in Sri Lanka.