The bodies of two deceased siblings, aged six and 10, have been found at a home in Perth's northern suburbs.

The children's mother is under police custody in hospital.

WA Assistant Commissioner Paul Steel said the woman was arrested at a nearby beach at about 8:40pm on Friday night.

"It appears that she has self-inflicted wounds that are non-life threatening," Mr Steel told reporters on Saturday.

"As a result, she is not able to be interviewed at this time.

"This is a tragic event and our heartfelt condolences go out to the friends and family of the children.

"Tragically for first responders, finding the bodies of two young children would have been a terrible thing to have to go through."

Police were called to the Bogdanich Way property in Madeley at about 6pm on Friday, responding to calls from concerned neighbours.

Homicide detectives and forensic police are investigating the circumstances surrounding the deaths.

Mr Steel said the children's father was helping with the investigation.

Police say they have no information to indicate there is any ongoing threat to the public.

Readers seeking support can contact Lifeline crisis support on 13 11 14, Suicide Call Back Service on 1300 659 467 and Kids Helpline on 1800 55 1800 (for young people aged 5 to 25). More information is available at Beyond Blue.org.au and lifeline.org.au.