Another shopper spotted the babies, believed to be nine months old, and after realising their mother wasn't coming back in a hurry, took matters into her own hands and got them out of the hot car.
She has since reported the incident to police and spoken to the New Zealand Herald about why she effectively broke into a stranger's car and removed her children.
It was about 20 degrees Celsius in Auckland yesterday and humidity was at least 88 percent when the woman and her mother left Westfield in St Lukes and went to their car.
"We got to the car at 3pm and I saw the babies. At first I thought the parents must be just putting a trolley away but no one came," the woman who asked not to be named, said.
"The babies were getting more and more distraught. I thought the car was completely locked but then I saw the window was covered by a shade and was open. I reached in and managed to open the door and took the babies out. I held one and my mum held the other and we waited for their parents to get back ... it was about 3.30pm when she sauntered over."
The woman said the babies were hot, sweaty and distressed.
Mall security staff had come over and arranged for the owner of the vehicle to be paged over the public address system inside the mall.
"The babies were getting more and more distraught," said the woman.
"The mum got back at 3.30pm and said she parked at about 2.50pm. She said 'I was only going to be 10 minutes'. She had Kmart bags ... she hadn't heard them paging her. She said she felt terrible and 'you probably think I'm a bad mother'.
"Then she said, 'I tell my husband all the time that you can't leave your babies in the car in this country, they just go off at you'. Then she said 'I purposefully parked the car undercover and in the shade ... they normally sleep for ages'."
The woman, who has young children of her own, said she did not want to judge the other mother, but was horrified at her explanation and excuse.
"Sure, we have all left our kids in the car to whip into the dairy to get milk or when we are paying for petrol but you don't leave them in a mall carpark," she said. "And when she said 'they normally sleep' - does she do this all the time? I don't think the mother understands the impact.
"What if someone had crashed into her car, stolen her car or taken the children? What if something had happened to her in the mall and nobody new these babies were out in the carpark. I didn't sleep all night. I rang the police this morning on behalf of the babies - someone needs to know."
Police told the woman they would contact the owner of the car and speak to them.
Westfield spokeswoman Deb McGhie said security staff watched for situations like this and there were procedures in place.
Westfield staff did not initiate removing the children from the car. "Obviously this woman was concerned and did what she felt was right at the time."
Ms McGhie said the babies' mother told staff she had "whipped into the centre for what she thought would be a couple of minutes, but she got detained".
"Everyone was okay, everyone went home happy."
Ms McGhie said centre management were looking into the matter to see if any further action was required.