Accused teenage murderer Teancum Vernon Petersen-Crofts has a long history of mental health issues, his father has confirmed.

Awatea Crofts said his son had been admitted to several mental health facilities in the past - but had never received the appropriate medical help, ABC News reports.

Even throughout this year, his son was in and out of mental health facilities and recently his condition had declined.

Petersen-Crofts appeared in a Perth court on Monday after being charged for the death of his mother, Michelle Petersen, 48, her daughter Bella, 15, and son Rua, 8.

The bodies of his mother and Rua were discovered inside their Ellenbrook home on Sunday. Bella was found critically injured in the backyard. She died on the way to hospital.

Local media have reported that Petersen-Crofts had presented at a Perth hospital in a "psychotic state" on Saturday night but was turned away after police became involved.

In early 2015 he was hospitalised in Christchurch after a series of ongoing mental health episodes, Crofts told ABC News.

"It was very difficult for him and the mental health staff. It was a perpetual, continual episode after episode.

"His mother did everything she could and just in the last days, her last six months, she was still doing everything she could but his condition had blown right out," he said.

Crofts believed that police were often at the residence and that his son had also been rejected from mental health services before, ABC News reports.

Western Australia Police Commissioner Chris Dawson has confirmed that the family was known to police before the murders occurred.

Petersen-Crofts remains in a psychiatric facility at Graylands Hospital and will face Stirling Gardens Magistrates Court next week.