Dr John McMenamin, of Wicksteed Medical Centre, said children exposed to smoke were more likely to have ear infections, coughs and colds.
"Over a longer time [they] can experience lung damage and cancer risks.
"It is easy to overlook the fact that children in a car with a smoker are also smoking themselves," he said.
Dr McMenamin said about 300 people died from passive smoking each year.
"We increasingly recognise lung disease and cancers that have been diagnosed in non-smokers who were exposed to smoking as children.
"We now include passive smoking as part of our regular health screening for both adults and children, and include this history when evaluating a patient's future health risks."
Mrs Turia said a proposed ban was about "ensuring that our tamariki are not exposed to second-hand smoke".
"It is a policy that we have seen implemented in Queensland, Australia, and I have asked my officials to look into this and how this may work here in New Zealand."
A Parliamentary bill increasing the price of cigarettes to more than $20 a pack over the next four years was passed earlier this week.
The legislation will raise tobacco excise tax by 10 per cent each year from 2013 to 2016.
The tax hikes are part of a raft of measures designed to make New Zealand smoke-free by 2025.
In July, tobacco displays in retail outlets were banned and proposals for plain packaging of tobacco products are currently being considered by the Government.
Plunket says any exposure to smoke is harmful for children.
"Second-hand smoke makes children sick. It flattens the little brushes that sweep and clean their airways," clinical advisor Allison Jamieson said. "Because children breathe faster than adults and have smaller bodies, they take in a higher dose of smoke than adults.
"In confined spaces, such as cars, they are unable to move away from smoke and are trapped with its poisons."
Michael Coulhoun of Action on Smoking and Health said young children were most vulnerable to the harmful effects of smoking.
"Unlike the restaurant and bars which had a high level of smoking and that's now been corrected, there's still an impact in cars.
"We think it will reduce the harm on smoking and ... the emphasis should be on young children, whether it's passengers under a certain age - certainly under 16." APNZ
HIGH RISK
children exposed to second-hand smoke are at increased risk of:
Premature death
Sudden unexpected death in infancy (cot death)
Chest infections
Ear problems
More severe asthma
Source: 2009 New Zealand Tobacco Use Survey
