Mila Tamihana, described by a family member as a "beautiful little angel", was found severely injured in the driveway of a Cartmel Ave, Massey, home at 12.37pm yesterday.
She lived there with her parents, Camita Broughton and Chadaz Tamihana, and her four sisters.
Police said family members found Mila and took her to Waitakere Hospital.
Doctors tried to revive the toddler, but her condition deteriorated quickly and she died.
Police investigating Mila's death said it could take days to establish what happened.
Detective Sergeant Eugene Pickett said last night it was unclear why Mila was in the driveway, who hit her and with what vehicle.
"At this stage we're speaking with family and neighbours, some of whom are understandably too distressed to speak to us yet."
Mila's grandfather, Harry Tamihana, last night said the family were distraught.
"Mum is blaming herself for not looking, but we don't know what happened, the police are investigating ... With this shared driveway it is really hard to turn around."
Mr Tamihana said Mila's aunt had taken her off the driveway earlier in the day.
Mila was the youngest of five daughters, the oldest aged 8.
"Mila was such a burst of sunshine. She's such a big part of our family. I would get here and she had such a strong voice and would come running out and greet me."
Mr Tamihana said everyone should take extreme care with children in driveways and around cars.
"You can't be vigilant enough. She was the youngest of five and now there is just four."
Ms Broughton and Mr Tamihana share the Y-shaped driveway with a neighbour.
Police would not say where in the driveway Mila was found, or where they thought she was hit.
She could have been in her family's section, the neighbours' or the shared part of the drive.
Safekids director Ann Weaver said Mila's death was tragic. She said the only way to prevent further deaths was to keep pushing the safety message.
"When we run a big campaign and talk about this a lot, the statistics tend to decrease," she said.
"But when it's forgotten for a while, then it starts happening again. What we have to do is continue to keep this in the forefront of people's minds."
Each year, at least five children die as a result of being hit by cars in driveways, and a child is hospitalised with injuries each week.
Mila's parents were too distraught to speak about her death last night.
They were being supported by a police iwi liaison officer and Victim Support.
Ms Broughton's sister, Aleishah, posted a message on Facebook hours after Mila died.
"Rest in peace our beautiful little angel Mila," she wrote. "Aunty can't describe the pain and hurt we are all going through, especially your mummy and daddy and four sisters.
"Honey, God has called you home too soon ... I feel numb, in shock, upset ... Your cousins are going to miss you like crazy."
Aleishah Broughton posted a second message soon after, apparently taking exception to people making comments about her sister's care of Mila.
"My sister is the best mother out. You don't know the full story."
Neighbours did not know of the tragedy until police arrived.
Mrs Weaver said the "glorious" weather meant many people were leaving doors open, which increased the chance of tragedy.
"It's very easy for a child to run outside so quickly, without you realising they have disappeared."
