A 15-year-old boy has pleaded guilty to sexually assaulting, robbing and bashing an 83-year-old Perth woman after breaking into her southern suburbs home.

The teenager admitted a total of nine charges when he appeared in the Perth Children's Court on Tuesday afternoon via video link from Banskia Hill detention centre.

The offences included four counts of aggravated sexual penetration, one charge of using violence to gain money and one count of assault causing bodily harm.

The boy was arrested in October, two days after forcing his way in to the elderly woman's home in the early hours of the morning and repeatedly sexually assaulting her.

He also physically assaulted her and fled the scene after stealing her handbag.

The woman was taken to Fiona Stanley Hospital where she spent one night before being discharged.

Alcohol syndrome assessment

At the time police said the crime highlighted the need for people, especially those who live alone, to make sure their homes were secure and for neighbours to watch out for each other.

The boy said very little during his court appearance, other than he understood the charges against him and to enter his pleas of guilty.

Prosecutors successfully applied for him to be sentenced by the President of the Children's Court because of the seriousness of the offences.

The teenager was remanded in custody until he appears in court again next month, when a sentencing date may be set.

A neuropsychological report on the teenager will be prepared for the hearing, and he will also be assessed to determine if he has foetal alcohol syndrome.