Father charged with murdering his two children

A Perth father has been charged with murdering his two children after he was found in his home with self-inflicted stab wounds.

The three-year-old boy and five-year-old girl were found dead in their Perth home after being seen by neighbours only hours earlier on Thursday looking like normal children happily playing on the front lawn.

The children's 35-year-old father, Jason Headland, was found inside the home suffering stab wounds and was taken to hospital under police guard on Friday night in critical condition.

It is understood Mr Headland slashed his throat, but did not inflict similar injuries on his children.

The distraught grandmother of two children found dead in the apparent murder-suicide has urged people suffering depression to get help.

"I thought I had a dream or something but when you face it and it is real ... it just hits you, especially with two little ones, grandchildren ... where do we go from here?" the grandmother, identified only as Georgina, told ABC radio.

"If you are having problems, if you are feeling depressed, please God, talk to someone about it."

Police Detective Inspector Peter Clements said the investigation was in its infancy so he could not say what had happened or why.

But police believe the father is responsible and his injuries were self-inflicted.

"His injuries were fairly significant requiring some fairly intense medical attention," Det Insp Clements told reporters.

"We are still investigating the circumstances around why we were there and how we ended up there," he said.

The children's mother also lived at the home but was not present when police were called, had to force their way in and were confronted with the grisly homicide scene at the home at coastal Yanchep on Perth's northern outskirts at 10.30pm on Thursday.

"We have a family liaison officer appointed to her, we are in direct contact with her now, she is obviously very, very distressed," Det Insp Clements told reporters.

"We are doing what we can at this point to provide support not only to her but the police officers who attended, it was obviously quite distressing."

A next door neighbour told he heard a scream while having dinner at 6.15pm but thought it was from the TV, which he later told detectives.

"I heard a girl's voice or a woman's voice, high pitched and a scream," he said.

The family had moved in about 12 weeks ago but he had not seen the mother, who was a mining fly-in fly-out worker, and said the father kept to himself.

The neighbour, who did not want to be named, said the children were seen playing on the front lawn on Thursday afternoon, hours before they were killed.

The street Flight Vista is in a golf course estate with many properties still under construction and residents who are new to the area.

Bunches of flowers have started to be placed in the street.

If you are concerned about the mental health of yourself or a loved one, seek support and information by calling Lifeline 13 11 14, Mensline 1300 789 978, or Kids Helpline 1800 551 800