A woman is believed to have killed two of her children before taking her own life.
Mother-of-five Melanie Stephens, 36, is thought to have suffocated Philip, five, and two-year-old Isaac and then hanged herself at their home in north Wales.
Police forced their way into the property in Trawsfynydd, Gwynedd, on Sunday night after frantic relatives were unable to get in.
A Home Office pathologist was last night conducting post-mortem examinations to establish the cause of the deaths, although it is understood police are not looking for anyone else in connection with the incident.
Ms Stephens had lived at the house in Chapel Street for about two years, having moved from the nearby town of Blaenau Ffestiniog.
Philip, known as Pip, attended primary school at Ysgol Edmwnd Prys.
Her three older children are thought to live with their father.
Residents in the village, which has about 700 residents, said the family seemed "happy and pleasant".
A neighbour, who did not want to be named, said: "Obviously everybody in the village is shocked. But nobody knows yet what caused this tragedy.
"I didn't know her very well because she wasn't from the village and I don't think she had many family here.
"But you would see her in the street and she would always say hello. They were a very pleasant family and seemed very happy. It's a terribly sad thing."