One charge involved the man punching the boy about 10 times in the head and face, with his head against a wall that cracked.
In the second, most recent case, he had punched the boy about four times.
The father had told police he remembered the incidents but would not elaborate.
Regarding one he said, "Can we just hurry up and get me to court?'' and for the other he said, "No comment''. He also said: "Things are changing, things have been changing. I'm not the best father but I'm trying.''
Judge Hobbs found the man not guilty of five other charges - one of assault by pulling the boy's hair or ear, and four of assault with a weapon, namely a broomstick, a vacuum cleaner pipe, a plastic tennis bat and a slipper.
He is due for sentence on November 9.
Judge Hobbs said he had considered section 59 of the Crimes Act 1961, which applied at the time of the offences and addressed parental control and reasonable force.
The judge said he was "satisfied beyond reasonable doubt that the force used was neither reasonable nor was it for any of the purposes set out in [the Act]''.