Katherine, 5 and 14-month old Harry, who was in a pram, were struck by the vehicle as they crossed a street with their mother in Cabramatta in southwestern Sydney on Wednesday.
As of Friday, a fundraiser for parents Sok Ram and Vun Dy Tha had raised over $330,000, with donations from more than 5500 people.
Organiser and family friend, Patrick Te said the outpouring of kindness had left him speechless.
"In the middle of such pain, we've created a small but powerful win — a testament to love, unity, and compassion," he wrote on the fundraiser page.
"By the grace of God, we keep moving forward."
Ms Ram's grief was laid bare as she spoke to media the day after the incident, saying she wished it had been her who was taken.
"Two of them gone, my kids are gone," she told AAP through tears.
"Last night I felt very cold. My heart and my body - I am hurt everywhere."
The 33-year-old said her daughter dreamt of growing up to become an artist or a teacher, while her son - who had just learned how to walk - loved kicking a small soccer ball around.
"I gave my kids everything, the big one (Katherine) she said 'Mummy and family more important than iPad'," she said.
The children's father explained the car had suddenly stopped, giving Ms Ram the impression she could cross the street safely, but then it struck them with children trapped underneath.
The 56-year-old man who was behind the wheel was uninjured and taken to hospital for mandatory testing.
Police said inquiries into the crash are ongoing, including whether the driver will face charges.
A number of witnesses tried to rescue the children, tipping the car onto its side to free them, Acting Superintendent Timothy Calman said on Wednesday.
Paramedics treated the children at the scene and they were rushed to hospital in a critical condition but died shortly after.
Premier Chris Minns said everyone was heartbroken by the loss of the two young lives.
"This is one of those tragedies that hit the community incredibly hard," he said.
Lifeline 13 11 14
beyondblue 1300 22 4636
Kids Helpline 1800 55 1800 (for people aged 5 to 25)
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