Elliott said George might have recognised her fatal mistake, but too late.
"The location of Ms George's body is consistent with a last-minute realisation that the car was still running and an attempt to reach the garage to turn it off."
She was found in the hallway, near the internal garage door, and there were blood stains on the floor where she fell, under her nose and mouth, perhaps indicating she lost consciousness and collapsed.
Elliott said: "Their deaths illustrate the importance of ensuring adequate ventilation and closing internal access doors when a car engine is turned on in a garage which is connected to a house.
"If a car engine is left running in a garage for too long, an open garage door may not of itself provide adequate ventilation and even a closed internal access door may not prevent carbon monoxide escaping into the house. It would be safer not to run a vehicle in a garage for any longer than is necessary to move it in and out."
The coroner also noted: "There have been at least three other deaths due to carbon monoxide poisoning resulting from the inhalation of exhaust fumes in a dwelling, although the circumstances were somewhat different in those cases."
Family and friends travelled from the Pacific Islands and Australia to attend a farewell service for George and her children, which followed a private family funeral.
Poko Ngaro, a cousin of George's, described her, at the service, as a devoted and loving mother. He said George had made Ashburton her home since leaving the Cook Islands in 2010.
The coroner said George was 32 and had lived in New Zealand since 2008, at first in Ashburton with her partner John Raukete, whom she married in 2011.
They separated in 2012, after which George went to Australia with her children before returning to Ashburton in 2013. Apart from a short period in Invercargill, she lived in Ashburton from 2013.
George and her children sometimes stayed at the house in Thomson St where they were found dead. The house's three usual occupants asked her to check the mail while they were away in the Cook Islands, and to run the Holden car so its battery wouldn't go flat.
"I told her to open the garage and start the car," one of the occupants said in evidence. "I told her to run the car for a couple of minutes and then turn it off and then leave."
"I didn't mention to her anything about ventilation as she had seen that I opened the garage door when I turned the car on to run it."
The coroner said that, on their return, the three occupants found George's van in the driveway and she and the three children dead in the house.
"The children were in the lounge and Ms George was on the floor in the hallway. The TV was on and the heat pump was set at 31 degrees. They rang emergency services."
The children were wrapped in fleece blankets as though ready for bed.
A neighbour told of hearing a car being revved at the house - three or four short bursts and a longer one as though the accelerator was flat to the floor - but all of this lasted less than a minute.
"The revving stopped and I didn't hear anything more. I don't know if the car was idling or turned off.
"I glanced over and saw that the garage door was down. I thought to myself that whoever was revving the car really shouldn't be doing that in the garage with the door down because of the fumes."
