One of the youngest people in Australia to be convicted of manslaughter could walk free from prison in just two months after he was sentenced over the stabbing death of Patrick Slater in the Perth CBD in the aftermath of Australia Day celebrations last year.

The boy was today sentenced to four years' juvenile detention but will be eligible for supervised release because of time already served.

The Perth boy was just 11 years old when he was involved in the death of 26-year-old Patrick Slater in the hours after last year's Australia Day fireworks.

Mr Slater's death was the culmination of a night of violence in Perth's CBD as fights broke out between the boy's group and Mr Slater's group.

He was stabbed in the chest with a screwdriver after members of both groups engaged in a rolling brawl on the city streets.

Most of those involved had armed themselves with a range of weapons including rocks, bottles, a socket bar, a piece of wood and a machete.

Earlier this year, eight other people including two other juveniles were sentenced to terms of between four-and-a-half years detention and life imprisonment over Mr Slater's death.

The boy, who is now 13, was originally charged with murder, but after a trial in the Perth Children's Court he was found guilty of the lesser offence of manslaughter.

Victim's family 'ripped apart'

In submissions today the boy's lawyer, Christian Miocevich, said his client planned to live with one of his older brothers, a fly-in-fly-out worker, when he was released.

Mr Miocevich said the boy hoped to continue his schooling at a local college, and also keep doing the sporting activities and cadets with which he had been involved while in detention.

Mr Miocevich told the court he had read to the boy the victim impact statement provided by Mr Slater's family, and the boy appeared "visibly affected" by what was said.

"He does wish to say sorry to the Slater family for their loss and for his involvement in it."

"He has been traumatised by what happened."

Outside the court, he added: "We just want to send our condolences to the Slater family and hope everyone can just take a step back and consider what the judge said, it's a time for reflection and not revenge."

Patrick Slater was killed during a brawl near the Perth Esplanade train station on Australia Day, 2016. ( Go Fund Me: Shaylee Cole Neil Winmar )

State Prosecutor Sean Stocks said Mr Slater's family had been "ripped apart" by his death, and was "struggling to deal with it."

Mr Stocks described what happened as "a truly senseless crime" that was the culmination of violence that appeared to have started for no obvious reason.

Mr Slater's uncle, Zakary Phillips, said the family was satisfied with the outcome and relieved the case was over.

"We're very happy with that even for a young boy, which shouldn't have happened in the first place," he said.

"It's been a hard journey it hasn't been an easy journey at all but hopefully we can get on with it."