A 16-year-old boy who was found bashed and unconscious in the Perth suburb of Balga at the weekend has died.

Quinn De Campe was found lying in a pool of blood in a bush reserve near the North Balga Primary School on Sunday afternoon.

He was in a critical condition when he was placed on life support at Royal Perth Hospital, but died overnight.

Mr De Campe was a student at Duncraig Senior High School.

A number of youths, among them Clement Wetnhik, found the unconscious teen while riding their bikes in the park.

"He was beaten up, he was on his own, I think the people who beat him up left him there," Mr Wetnhik said.

"He was just badly bashed and his eyes were half shut like he was dead and his hands couldn't move."

Police believe Mr De Campe and his attackers knew each other and had arranged to meet at the park.

Teenagers charged with grievous bodily harm

Yesterday, police charged a 16-year-old boy with causing grievous bodily harm.

Sergeant Naomi Smith says another three teenagers have since been charged over the bashing.

"They've charged a 16-year-old from Warnbro, a 16-year-old from Westminster and a 15-year-old from Marangaroo," she said.

"All three teenagers were charged with one count each of aggravated robbery and [causing] grievous bodily harm.

"The juveniles were remanded in custody."

The three appeared in Perth Children's Court this morning but did not enter a plea or apply for bail.

They have been remanded in custody until their next appearance in court with one of the three due to appear on Friday while the others accused will be back before the courts in January.

It is understood charges may be upgraded once a post-mortem is conducted.