A 16-year-old boy has denied murdering his mother and stabbing his younger sister in his first court appearance. The teenager appeared via video link in Perth Children's Court on Wednesday, one day after the alleged attack in the Perth suburb of Bentley.

During his initial hearing, the magistrate stated, "On the 21st July in Bentley it said you murdered (your mother)." The boy responded, "Why would I do that? I didn't do that," appearing visibly upset. The magistrate also noted a charge that the boy "attempted to unlawfully kill (your sister)."

The court appearance, during which no pleas were entered, followed the discovery of the 35-year-old mother's body at the family home on Tuesday morning. The 12-year-old sister reportedly fled the home with multiple stab wounds and received life-saving first aid from passers-by before being taken to Perth Children's Hospital. She remains in stable condition and is receiving care for serious injuries, according to WA Police Commissioner Col Blanch.

The boy, who cannot be named for legal reasons, has been remanded in custody at the Banksia Hill Juvenile Detention Centre. He initially refused to face the video link for his second appearance but was eventually coaxed to do so. No bail application was made, and he briefly walked away from the camera during the hearing. He is now in the care of the Department of Communities.

Legal Aid has requested a senior lawyer to represent the boy on his criminal charges and a second lawyer for child protection proceedings. A mental health assessment and a report from the communities department have been ordered before his next court appearance, scheduled for August 5. Court staff have been instructed to explain the proceedings to the boy.

Police are treating the incident as "a family violence homicide against family members." The boy was known to police. Western Australian Premier Roger Cook described the event as "troubling" and expressed his condolences to those affected.