In one bizarre moment, which was captured on camera, one of the girls begins to dance on top of the car, which is then mimicked by a man watching.
Shopper Janine Clelland, who filmed the incident taking place, told the Gold Coast Bulletin the children had also spat on security and damaged the car.
"Apparently these girls were foster care kids and rebelling against something," she said.
"We didn't see it start, we just saw these girls jumping on the roof and bonnet of the carer's car. They were swearing and spitting at security and other people in the car park."
Witnesses then said police officers turned up and the attitude of the girls suddenly changed.
"They were just screaming 'we know the law you can't touch us'," witness Jonni Row told 9 News.
"But their tail was between their legs as soon as the cop car pulled up."
A police spokeswoman said they were aware of the incident but no complaint was made.
It's understood the children were dropped back at their carer's address later on.
Westfield has declined to comment.