According to the summary of facts, three boys were walking past the pair's house when one of them stole a pair of shoes from outside the front door. Robert Simpkins tried to grab him, at which point the boy threw the shoes away and ran off.
One of the remaining two went to return the shoes but the man punched him in the chest. The father and son then got into a car and chased the two boys.
When they caught up with them, Ngarimu Simpkins grabbed one by the neck and forced him into the car and continued to search for the other boy. On finding him, Ngarimu Simpkins pinned him on the ground and punched him in the head more than once. He then kicked or punched him in the stomach.
His father also kicked the boy in the stomach.
The boys tried to tell the pair it wasn't them that stole the shoes, but they forced one boy into the car to search for the boy responsible.
The chase continued, witnessed by members of the public.
During this time, Ngarimu Simpkins again punched one of the boys in the face, knocking him to the ground.
Members of the public intervened, with one man so upset by what he saw he struck Ngarimu Simpkins and the car with a metal bar.
Both boys were taken to hospital where they were treated for injuries. The third boy was uninjured but shaken.
A few days after the incident, the men told police they had intended to round up the boys who stole the shoes and take them to the police station.
"Both defendants stated that they were sick of all the petty theft occurring in their neighbourhood," the summary stated.
Both men had previously appeared before the courts, although not for violence.
In October, Rotorua Boys' High School principal Chris Grinter told the Rotorua Daily Post the school had no intention of standing him down.
When asked yesterday whether Ngarimu Simpkins would remain in his roles at the school following his guilty pleas, Mr Grinter said he had no comment.
The pair were remanded on bail for sentencing on August 26.
