Officers will be able to use their discretion to give warnings, refer people to quit smoking support services, or issue an infringement fee of $50.
A police spokesperson said officers have discretion around how they uphold the law.
"Compliance can be achieved through effective education, referral, and engagement, as well as enforcement."
Plunket NZ is in full support of the ban, however, said it will require community support to help parents and caregivers to not just stop smoking in the car, but give it up.
Chief nurse Jane O'Malley said the evidence was overwhelming that exposure to second-hand smoke was a major risk to children's health.
Second-hand smoke has been linked to many illnesses experienced by children including respiratory infections, asthma attacks, sudden unexpected death in infancy, glue ear and more.
Young children have no way of influencing drivers or adult passengers if they are travelling in a vehicle with a smoker, she said.
Dr. O'Malley said 23 per cent of the children Plunket see live with a smoker in the house when Plunket first visits them as a newborn.
Statistics are worse for those living in high deprivation, with 40 per cent of children living with a smoker in the family, she said.
According to SmokeFree NZ's website, children can get particularly sick if they breathe in second-hand smoke because their lungs are smaller, they have a faster breathing rate and their immune systems are still developing.
In confined situations, they often have no way of getting away from the smoke.
Tauranga locals interviewed by the Bay of Plenty Times yesterday supported the law, saying it was a 'great idea" and that the habit should not be "forced upon children".
Paul Kliess from Ohauiti said the law is long overdue and should really have been brought in a number of years ago.
Toi Te Ora's Medical officer of health Phil Shoemack said health professionals have been advocating for a law of this nature for a long time.
He said a law that is protecting children, specifically from something they are not a part of, is one that is very hard to argue against.
Dr Shoemack said there is no doubt that children living with an adult who smokes have much higher hospitalisation rates and are more likely to develop respiratory illnesses.
This new law along with raising prices, face-value advertising and the buying age of 18 are all great steps towards the national goal of Smokefree 2025, he said.