Martin Cutbill, whose son Tom suffered serious bite wounds to his right leg while playing in his grandmother's garden, said he was "disgusted" at the incident.
West Midlands Police issued an unreserved apology to the Cutbill family after Tom was attacked on Sunday during a search for metal thieves in the Oldbury area.
Speaking at the family's home in Rowley Regis, Mr Cutbill, 40, said he was "completely and utterly shocked and amazed" at what had happened to his son.
Asked how Tom was recovering after his ordeal, his father told reporters: "He is only recently out of hospital - he's only starting to take his first steps on crutches.
"There were quite a few puncture wounds and tears to the skin. He's had two operations, one to clean up the wounds to stop the risk of infection and the next one to seal the wounds."
Mr Cutbill, who works as a warehouse manager, added: "We have not really had much contact with the police yet and will be speaking to them tomorrow."
The West Midlands force has informed the Independent Police Complaints Commission, and is carrying out its own investigation into how the boy came by his injuries while the dog, a German shepherd-Belgian Malinois cross, was on a leash.
The dog's handler had been sent to support fellow officers who were searching an area near Western Road, Oldbury, for four men seen running away from a quantity of copper wiring.
Chief Inspector Ian Marsh said: "This poor young boy has gone through an absolutely horrendous ordeal and my thoughts are with him and his family as he recovers from his injuries.
"We apologise unreservedly for what has happened and have launched an investigation to fully understand exactly how an innocent young lad came to be bitten by a police dog in the safety of his own back garden.
"Police dogs and their handlers receive intensive training and play crucial roles in the arrest of suspects day in, day out, but on the very rare occasions where things go wrong, it's vital we understand why and learn the lessons to ensure it doesn't happen again."
The officer and the dog involved in the incident continue to carry out regular duties after an initial independent assessment.