A 42-year-old man has been charged with the murders of a 34-year-old woman and a two-year-old child, police said.
The pair, named locally yesterday as Suzanne Jones and her son William, were declared dead at the scene at an address in Porthmadog, Gwynedd, on Friday night.
North Wales Police said a local man was charged with the murders following a "domestic-related incident".
A spokesman for the force did not name the man.
Police said they were not looking for anyone else in connection with the inquiry.
No formal identification of the bodies has been made and a major incident room has been set up.
Family members are being offered support by specially trained officers, North Wales Police said.
Neighbours said Mrs Jones also had two daughters, Antonia and Amy.
David Thomas, 66, from the nearby village of Penmorfa, said he had known Mrs Jones since she was born and had been at her house last week.
He said: "Susi was born in this house here and she was a lovely girl who fitted into the community.
"You could not wish for a better full-time mother with the children."
Arthur Edwards, a retired factory worker who lives two doors from the terraced house outside Porthmadog where the incident happened, told of his shock at the news.
Mr Edwards, 76, said yesterday: "They kept themselves to themselves, as people do nowadays.
"I only fully found out what happened at 8.30 this morning when I received a text message and came out and asked."
"The boy William was such a happy little thing."
Another neighbour, who declined to be named, described Mrs Jones as an "absolutely dedicated mother".
Outside the house, which is set between mountains known as the Tremadog Slabs and fields with sheep grazing, friends and neighbours laid flowers.