Asthma nurse explains the effects smoking in cars has on kids

There are renewed calls for Parliament to introduce a ban on smoking in cars with children on board - and a nurse has told Newshub just why so many think it's a necessary change.

It's a big problem, with surveys suggesting one in five children are exposed to smoke in cars each week - that's 100,000 children.

It can cause respiratory infections, ear infections, asthma, sudden unexpected death in infancy, and also increases the risk of cancer.

Asthma nurse educator Elaine Murray says children are particularly vulnerable.

"Their lungs are very small and still developing, and they do breathe a lot faster than adults - so if they're breathing in secondhand smoke, they're going to be breathing in a lot more of those particles."

Smoking in cars with children is banned in the UK, Australia, South Africa and parts of the US and Canada.

The Children's Commissioner says a ban is easy to do, and would help prevent harming the health of 100,000 children.

There is clear evidence smoking is harmful, but there's still no law stopping people smoking in cars with children in the back.

"We've got to stop it, ban it, move on it," Children's Commissioner Judge Andrew Becroft told The AM Show on Tuesday morning.

It's banned inside workplaces, restaurants and bars, and Judge Becroft says it's shameful we're not protecting children in cars.

"We enacted the workplace ban on smoking because it affected adults - but when there's demonstrable evidence of the bad health effects for children, we're not acting."

A Health Select Committee recommended a ban here, but it was rejected by the previous National government.

Labour's testing whether there'd be support across Parliament, but it's not making any promises either.

Jacinda Ardern told The AM Show they're looking at the wider problem.

"If you smoke in your car then you probably smoke at home, and you may have smoked while pregnant - and all of that has an impact on kids.

"The best thing we can do is try and have families stop smoking altogether."

The Government's meeting with the Children's Commissioner this week to discuss stubbing out the practice.