'He wouldn't usually behave like this, but I've got to admit - it was a really bad tantrum. Probably one of the worst I would have seen,' she told The New Zealand Herald.
Mother-of-three Rebecca said that the older woman, who was also waiting in the queue, lost patience at her son’s tantrum and she turned around to see see her allegedly pushing a trolley straight towards her son.
When the mum moved to stop the trolley attack, the elderly woman apparently started abusing her, telling Rebecca to 'take him bloody home'.
After the alleged attack, the mum spoke to Kmart staff and said that CCTV footage allegedly shows the woman appear to steer her trolley into the young boy. And it was then that the staff member delivered another shocking blow.
'He said to me, "I'm sorry to do this to you… but I feel it's the right thing to do",' she said.
'We've reviewed the video footage in detail and we can see that she has actually punched your son in the head with quite some force, when your back was turned.'
A spokesman for NZ Police confirmed that they’d launched an investigation.
'Police were notified on Thursday afternoon about an earlier incident where an assault was reported to have taken place,' a spokesperson told Daily Mail Australia.
'Police will be looking into the matter and will be following up with the complainant.'