The 16-month old died on January 16 in a vehicle in the carpark.
A woman is believed to have left the boy in her car that day, mistakenly thinking she had dropped him at daycare.
The police investigation into the infant's death is ongoing.
The fatality has brought back a nightmare for Ashish Macwan.
His 3-year-old son Aarush drowned when the van he was strapped into rolled over a bank and landed in a cold South Island lake during a family holiday in April 2011.
Macwan had left the handbrake off while he had got out to stretch his legs at Lake Dunstan.
His wife, sister-in-law and their children were able to escape the van.
Macwan, a business lecturer from Auckland, said he could empathise.
"I can understand her struggle," he said. "When I heard about the tragedy in Wanganui, I immediately thought of my own son.
"I blamed myself for a long time afterwards. In my own mind I thought other people were blaming me, too. It was a daily torture I thought would never end."
After the accident, Macwan was discharged without conviction at Manukau District Court after being charged with careless driving causing death.
"People thought how terrible it must have been dealing with the police as well as all the grief. But at the time I was in so much pain that any potential punishment seemed nothing in comparison."
Macwan said a turning point came with the birth of his daughter Aashka, who turned 3 last month.
"Aarush was our only child when he died and family relationships were really tested afterwards," he explained.
"You keep asking yourself how could this have happened and wondering if you are a bad parent.
"Our daughter has given us focus. It helps when you have someone else to give your love to."
Macwan believed the woman would someday come to terms with what had happened.
"It is easy to say and difficult to do but you have to forgive yourself. I eventually found some peace again but I had to find someone close I could connect and share my feelings with, someone who would not be judgmental.
"[She] will eventually work her way through this."
- by Russell Blackstock of Herald on Sunday
