The baby boy died in hospital on Saturday night, Australian news outlet The Age reports.
His death came as Melbourne’s Jewish community mourned the death of 10-year-old Thalia Hakin who died on Friday after a driver allegedly sped through Bourke Street mall in a ramming attack that killed four and left dozens injured.
Two men, aged 25 and 33, and a woman, 32, also died on Friday.
The alleged driver, Dimitrious “Jimmy” Gargasoulas, remains under police guard in hospital.
He is yet to be interviewed by police.
Thirty-seven people have been treated in Melbourne hospitals after the attack. Four remain in a critical condition.
On Friday, former Victorian police commissioner Christine Nixon revealed after the out-of-control car had missed her by less than a meter, she saw an upturned pram on the side of the road.
She went to check and found that it was empty.
The distraught mother had reportedly asked: “Where’s my child?”
It is understood three children remain in hospital.
Two adults and a child died, 15 people were injured after a car drove into pedestrians along the mall in Melbourne center on Friday. A fourth person died in a hospital on Friday night.