The parents of the infant Bourke St victim recall the moment they said goodbye.

It was the most haunting image of the Bourke Street Mall tragedy: a pram laying overturned and empty on the side of the road, as chaos reigned around.

Before 26-year-old driver Dimitrious Gargasoulas allegedly careened through Melbourne’s CBD that deadly January afternoon, that pram had held two sleeping children.

Two-year-old Zara was injured but survived. Her little brother, Zachary did not.

For the little pair’s mother, Nawwar Hassan Bryant, that image of the pram tears at her fragile heart.

“It reminds me of a life I once knew,” she told A Current Affair, “a pram that carried both my children everywhere I went.”

The day - January 20 - had been a happy one. Nawwar had taken Zara and Zachary to visit a museum with the help of their part-time nanny, with whom she then left them while she ran an short errand.

But when she called to check in some five minutes later, everything changed.

"When [the nanny] picked up the phone, that was when my nightmare started," Nawwar told A Current Affair.

"She answered the phone and said, 'Something bad has happened.' I just asked her, 'Where are my children?'"

Both had been rushed to Melbourne's Children's Hospital - Zachary in the back of a police car. The three-month-old was taken into theatre, but there was nothing doctors could do. His little body had simply been through too much.

"It was horrible," Nawwar's husband, Matthew Bryant, told A Current Affair.

"Even when they all walked in and said he was brain dead, it was just surreal. Literally that morning I was playing with him in the living room and then the next minute you've got a doctor telling you that he's clinically dead."

The couple say they will be forever grateful to hospital staff for allowing them the space and time to come to terms with his death, to hug him one last time.

"Even though we knew we were holding a lifeless baby, but we knew that he was ours and we had to say goodbye," said Nawwar.

"That was really lovely and we were blessed to have that chance to be surrounded by so much love."

While she knows the void left by Zachary's death will remain for the rest of her life, Nawwar can't help but smile when she speaks of him.

"He was the absolute light of our lives. He was absolutely perfect," she said.

"From the moment we knew we were going to have him, right up to the time we laid him down to rest."

Dimitrious Gargasulous has been charged with five counts of murder.