Reid Steele died at University Hospital of Wales in Cardiff on Thursday afternoon after being found at a house in the Welsh town, and police are treating the death as murder.
In a statement after police released the boy’s name, his family described him as a “super happy, gorgeous, wonderful and intelligent” child.
A 31-year-old woman was arrested on suspicion of his murder and she has now been transferred into the care of health services and is being detained under the Mental Health Act.
The family added: “He was a super, super-happy, gorgeous, wonderful and intelligent little boy who lit up everyone’s lives.
“He loved the garden and the beach, picking raspberries and going for walks collecting shells. He was a very chatty little boy and would happily speak to anyone.”
Detective Chief Inspector Matt Davies said: “We are dealing with a very sad and tragic incident.
“The family continue to be supported by dedicated family liaison officers and once again, I would appeal for members of the public to refrain from speculating on social media at what is a very difficult time for all concerned. My thoughts remain with the family.”
The force said it is not looking for anyone else in connection with the incident.