Three boys have been arrested after riding a dirt bike across an oval in Armadale where kids were playing soccer before allegedly threatening people with a knife and fleeing with a spectators handbag.
Police spokesman Adam Brouwer says around 10.15am on Sunday, two boys aged 13 and one aged 12, rode a red motorcycle onto Morgan Park where up to 200 kids were playing soccer matches.
"At one point the boys rode the motorcycle near a spectator, stealing her bag," Mr Brouwer said.
"As the boys attempted to leave the area, a number of witnesses attempted to apprehend the them.
"At this time one of the boys produced a large knife and threatened witnesses."
The three boys were later located by police at homes in Armadale and Brookdale.
Armadale Soccer Club junior secretary Cherie Alvaro said a number of kids were clearly shaken after the incident.
"They were spooked and ran to their coaches," she told Radio 6PR.
"A few of them were crying and some of them couldn't go back on when the game resumed because they were so shaken".
Ms Alvaro said it wasn't the first time someone had raided the match on a motorbike.
"It used to happen all the time, so the council put up a fence around the oval," she told WAtoday.
"But the kids got through a hole in the fence.
"A lot of parents chased after them but when we got back to the pavilion one of the kids said one of them had a kitchen knife, so I rang the police and told them to get their butts down here."
A 13-year-old Brookdale boy has been charged with stealing a motor vehicle, no authority to drive, reckless driving, aggravated armed robbery and acts of omissions like to endanger life, health or safety.
A 12-year-old Armadale boy has been charged with a string of charges, including stealing a vehicle and aggravated robbery.
A 13-year-Armadale boy has been charged with a number of offences, including possessing cannabis and common assault.
All three will appear in the Perth Children's court on Monday.
