An Auckland woman claims her son was attacked for throwing a tantrum inside Kmart Albany.
The mother posted on Facebook to say a woman, aged in her 60s, deliberately punched her son, moments before ramming him with a trolley.
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She told NZME she saw the unknown attacker ram her son. When the mother stepped in the older woman unleashed a torrent of verbal abuse.
"Everybody had just stopped, and I was quite surprised afterwards when I realised people don't interfere, in case something else that's bad happens.
"I think people were just kind of staring and watching, while she laid into me."
The mother only found out her son had been punched when Kmart staff called her later in the day to let her know.
"[The store manager] said to me, 'I'm sorry to do this to you... but I feel it's the right thing to do'.
She says the manager said they reviewed the video footage in detail and could see that she had punched her son in the head with "quite some force".
She has formally complained to police, who confirmed to Newshub an investigation has been opened.
"Police were notified on Thursday afternoon about an earlier incident where an assault was reported to have taken place," a spokesperson said.
"Police will be looking into the matter and will be following up with the complainant."
Newshub has contacted Kmart, as well as the mother for comment.