Sixteen family and friends of the deceased attended Melbourne Magistrates Court to watch Cai Liao's 17-minute appearance at a filing hearing.

Ms Liao, 45, is alleged to have attacked the boy, Alistair Mach, with garden shears and then lay in wait for his grandmother at a house in Albanvale.

An earlier hearing was told that Ms Liao waited 10 hours for Mai Mach, 60, to return from work and then attacked and killed her with the shears.

Detective Leading Senior Constable Tony Harwood told an out of sessions hearing on Wednesday night that Ms Liao had been in a relationship with Ms Mach's husband Brian March, 61, for three years when his marriage broke down.

Mr Mach, who had recently ended his relationship with Ms Liao, was found bound and gagged in the house on Tuesday.

Detective Harwood said that when Ms Liao, a Chinese national in Australia on a tourist visa, arrived at the house at 6am on Tuesday, an argument began between her and Mr Mach.

Ms Liao was alleged to have bound and gagged him and then entered the bedroom where Alistair - who was being babysat by his grandparents - was in bed.

She allegedly attacked him, and an autopsy found he had received 18 wounds, some of which were defensive.

Ms Mach was found to have sustained 23 wounds.

Ms Liao, of Albion, is charged with two counts of murder and also intentionally causing injury, unlawful imprisonment and assault.

In a black jumper, she was led into court and sat next to a Cantonese interpreter with two custody centre guards as prosecutor Luke Excell told Chief Magistrate Peter Lauritsen she had been charged on April 1.

As Mr Excell announced further administrative dates, Ms Liao, who did not once lift her head, nodded to the interpreter and began to sob.

Her sobbing grew louder and continued as her senior solicitor Sarah Pratt said her client was on medication for blood pressure, it was her first time in custody and she had instructed she had suicidal ideation.

Mr Lauritsen remanded her until July 22.

Ms Liao nodded slightly and was led away.

Alistair's parents - Mai Mach's daughter Amy Mak and Andrew Kwong - attended the hearing flanked by relatives.

The couple, who did not want to speak publicly, shielded themselves from media outside the Magistrates Court. They were escorted by homicide squad detectives and relatives to a waiting car.

As they were in court, distressed friends gathered at the family home in Maidstone, arriving with shopping bags brimming with food.

Family friends remembered Alistair as a "bubbly, outgoing" boy who loved to talk and explore. Neighbours of Ms Mak, who worked in urban planning with the local council, and Mr Kwong, a sales consultant in real estate, spoke fondly of the four-year-old.

Yen Nguyen said he was a "very happy boy".

"It's very shocking and sad. I feel so sorry for them," she said.

The day care centre where Alistair attended, Explorers Early Learning, expressed its distress over what happened to one of their pupils.

Executive coordinator Alicia Holmes told Fairfax Media that Alistair was a "very special little boy" who will be greatly missed by staff and children.

"We extend our deepest sympathies to Alistair's parents and family," she said.

Meanwhile, in the Albanvale street where Alistair and his grandmother were killed, neighbours were reeling after the gruesome details of what occurred so close to them were revealed in court.

"How did this happen in my street?" neighbour Tilda, who did not give her last name, said.

Mrs Mach was a well-known face at the Delahey Community Centre, where she attended computer classes. A family friend said she was "a very nice lady and a caring mum" who "loved Alistair and always helped out".

with Allison Worrall and Tammy Mills