"He ended up hitting my son with a closed fist in the side of the head."
Maddren said the pair quickly left without acknowledging the injury.
"The caregiver said nothing to us.
"All I can remember him saying was the man's name and then grabbing him and getting him out of the store as quickly as possible.
She said after the punch was thrown everyone was left stunned.
"It was quite a thump. He didn't even cry but he was confused about what had happened.
"Everyone was quite shocked that it had just happened."
"I understand him trying to get him out but if he just said I hope you're okay before he left it would have been understandable," said Maddren.
Fearing the worst Theodore was monitored closely for signs of injury for the next few hours. Later that afternoon he started vomiting and the parents were advised to take him to hospital. He has since been discharged with doctors suspecting he had contracted a virus rather than showing signs of delayed concussion.
At the time Maddren complained to the supermarket about the unprovoked attack and said she was taking the matter to police to protect other children.
"We don't want it to happen again to another kid," said Maddren.
Supermarket owner Quintin Procter said the incident was "terrible and unfortunate".
Looking at the camera footage, there was "no indication" the man was going to hit Theodore, he said.
"He just turned around and went 'smack'."
Procter said the caregiver had reacted instantly and "physically manhandled" the man out of the store.
He and his team were investigating the incident but had been unable to track down the man or his caregiver.
Police confirmed they are investigating an incident where an 18-month old was assaulted by an unknown man in a Wairau Rd supermarket.
