Trainor didn't wait for an ambulance, loading her son into a car and driving to Hawke's Bay Hospital in Hastings.
Trainor says she was told at the hospital that Maxin's wounds were the most severe dog bites they had seen.
The pair were then transferred by emergency flight to Christchurch Hospital for surgery.
Trainor told the Herald that effect of the attack on her family has been severe.
"My dad still breaks down about the state of my son when he picked him up. He said he can't get the image out of his head," Trainor said, revealing that she also struggles with the physical toll it has taken on her son.
"I have my up and down days," Trainor said. "I'm scared he's going to get a hard time about the scarring when he's older."
She said doctors are "not quite sure" if there is nerve damage and he faces ongoing surgery as he grows.
Tragically, Maxin is now aware of the damage he has received.
"He's only in the past couple of weeks now seen it. He was looking in the mirror the other day and he's now just discovered it," Trainor said.
She said he's distressed by his injuries, which he referred to his as his "ouchies".
Hastings District Council regulatory solutions manager John Payne told the Herald that the council's animal control team didn't hear about the attack until May 23.
He says that, when asked about the delay, the complainant said they understood the dog would be put down by its owner, but that didn't happen.
"Council has been attempting to investigate the matter, but no formal statement has been provided yet, and an investigation is still pending.
"Council did seize two dogs from the owner's property on June 10 but had no grounds to hold the dogs and they were released on June 11 on strict conditions," he said.
Payne told the Herald those conditions include the dog not being allowed to leave the property, unless in an emergency, and inspections by council.
The Herald contacted the owner of the property, who refused to comment but denied his dog was responsible for the attack.