There appears to be a bit of confusion regarding the smoking in cars laws at the moment. I think because the UK are just introducing the law where as it has been in place in NSW for quite some time.
According to NSW Health, “Smoking in a car with a child under the age of 16 is an offence under the Public Health (Tobacco) Act 2008. A $250 on the spot fine applies to the driver and any passenger who breaks the law and this is enforced by NSW Police.
Here is a link to the relevant NSW Health page and there is also a fact sheet to download