A spokeswoman for North Wales Fire and Rescue has confirmed that a third child has died of injuries sustained in a house fire in Prestatyn.
Charlie Timbrell, aged fifteen months, was the son of 20-year-old Lee-Anna Shiers who died in the blaze.
Two other children, Mrs Shiers' niece and nephew, also died.
A mother and her niece and nephew have died in a house fire in Prestatyn.
Neighbours tried in vain to rescue the family from their first floor flat late last night.
A 15 month old boy is in a critical condition in hospital, while the partner of the woman died is said to be in a 'serious' condition.
Our North Wales reporter Ian Lang reports from the scene.
The 20-year-old woman killed in the house fire in Prestatyn has been named as Lee-Anna Shiers.
Ms Shiers 15-month-old son remains in a critical condition at Alder Hey Children's Hospital in Liverpool, while her partner, 23, is in a "serious" condition at Whiston Hospital, Merseyside.
Neighbours of the victims of the house fire in Prestatyn have paid tribute to the 20-year-old woman who died.
The woman and her 23-year-old partner, who remains in hospital with serious injuries, were described as "the nicest... kindest... sweetest people".
"You don't expect this in Prestatyn", one man added.
North Wales Police say the two people in custody following last night’s fire in Prestatyn are a 45 year old man and a 42 year old woman. They have been arrested on suspicion of murder
– North Wales Police spokesperson
The property involved in the incident at Maes y Groes in Prestatyn is a house which has been converted into ground floor and first floor flats.
The victims of the fire lived in the first floor flat. Those arrested lived in the flat below.
We would appeal for anyone who may have seen anything suspicious in the Maes y Groes area of Prestatyn yesterday evening to get in contact as soon as possible by calling us on 101.
The 15 month old baby boy is said to be in a critical condition. He is the son of the 20 year woman who died in the fire and her 23 year old partner, who is receiving treatment for 'serious' injuries.
Police say the 20-year-old woman who died was related to the two children who died, but was not their mother. Her partner is not related to the two children who died.
A Welsh Ambulance spokeswoman said the man and baby were taken from the Prestatyn fire to Glan Clwyd Hospital.
The man was later transferred to Whiston Hospital, Merseyside. The baby was transferred to Alder Hey Children's Hospital in Liverpool.
Both were said to be in a serious condition.She described the property as a house that had been converted into flats.