"I think my husband is likely to need counselling he's so stressed, and distraught," she said.
The boy was rushed to Tauranga Hospital with life-threatening injuries on Sunday afternoon, then flown to Auckland's Starship Hospital that night.
He required surgery for what was understood to be extensive facial injuries before he was moved to a specialist unit at Middlemore Hospital for more surgery.
A Middlemore Hospital spokesman said the boy was in a serious but stable condition in the intensive care unit.
The boy's grandmother said her husband was now at their grandson's hospital bedside, as were the boy's parents who were also greatly distressed and too distraught to talk about their son's injuries.
"I didn't see the attack myself because I was inside and my daughter was using the wood chipper so there was quite a lot of noise going on at the time. It's been devastating for the whole family."
The plastic surgeon involved in the boy's treatment had declined a request to talk about the boy's injuries, surgeries and future treatment plans, without permission from the parents, the Middlemore Hospital spokesman said.
A police spokesman said the investigation into the attack was still in its early stages and it was too early to say whether any potential prosecution was likely.
The dog involved in the attack had already been put down after its owner voluntarily surrendered it to Western Bay of Plenty District Council animal control officers.
The council's compliance and monitoring manager Alison Curtis said there had been 13 reported attacks in the district in the past three months and 56 in the past two financial years. That included a 3-year-old boy treated at Waikato Hospital for a facial injury after being attacked by a dog in Te Puke on July 6.
Research showed any dog had the potential to attack and most attacks were committed by a dog known to the victim and likely to be a family pet or a relative's dog, she said.
Tauranga City Council animal services team leader Brent Lincoln said there were 69 attacks on people the last financial year, seven more than during the previous year.
So far this financial year there had been 18.
That included a woman who suffered a bad leg injury after a dog lunged at her while she was visiting a Papamoa property in August.
Mr Lincoln said the dog's owners were facing charges and were expected to appear in the Tauranga Registrar's Court later this month.
On Tuesday a dog owner was convicted and fined $600 in the Tauranga District Court after the dog took a chunk out the elbow of an elderly neighbour.
The judge ordered the dog destroyed. Mr Lincoln said recorded attacks related to any physical contact between a victim and a dog and included ripped clothing or even a scratch. "Every dog owner needs to be aware that they are responsible for the actions of their dog at all times, whether in the home, walking their dog down the street or exercising it on the beach.
"It is the owner's total responsibility to ensure their dog is controlled at all times.
"No matter how good people think their dog is with children, young children and dogs should never be left unsupervised."
