Police have confirmed a 35-year-old man arrested on suspicion of the murder of two children in Denbighshire is their father.
Caitlin and Aidan Samuel were pronounced dead at hospital
The man has been named locally as Perry Samuel.
Caitlin Samuel, five, and her brother, Aidan Samuel, three, were found at a house in Bodelwyddan near Rhyl just before 2300 GMT on Sunday.
In a statement, the children's family said: "We cannot express just how much we loved our two little angels."
The brother and sister were found at a house in Coronation Close by two female police officers after a 999 call was made. Mr Samuel was alone in the house when they called.
The children were taken to Ysbyty Glan Clwyd where they were pronounced dead less than an hour later. It is not yet known how they died.
Police called to the house after a 999 call by the arrested man
Detective Chief Inspector Dave Jolly said : "We are keeping a completely open mind about the cause of the deaths and we are pursuing a number of lines of inquiry.
"It would be completely wrong to speculate about the cause of death at this moment."
He described the children's family as "extremely traumatised".
A statement issued from the family read: "Following last night's tragic and incomprehensible incident, we are appealing directly to the media that they respect our wishes and that we are allowed the breathing space we so desperately need to come to terms with this terrible life-changing situation in private so we can mourn in peace and with dignity."
The house has been cordoned off by police tape. Flowers and soft toys, including a Winnie the Pooh bear, had been left by well-wishers.
Both children were pupils at Ysgol y Faenol school in Bodelwyddan.
Head teacher Martin Edwards said: "Our whole school community has been deeply shocked and saddened at this tragic loss.
"The two children were bright, popular and happy pupils and will be very sadly missed by their classmates and the staff at the school. Our thoughts and condolences are with the family at this time."
Neighbour John Bairstow, said there were a lot of children in the street who tended to play together.
"This is a family-oriented area. You have second generation people on this street, who grew up here and now have families of their own.
"It is terribly sad news, particularly as I'm sure this little boy and girl will have been well-known to the children and other families on this street."
The results of the post mortem examinations were expected on Monday evening or Tuesday morning, police said.
North Wales Police have appealed for anyone with information to contact them on 0845 607 1001 (Welsh language line) or 0845 607 1002 (English language line).