Scientists say that smoking in cars creates dangerous levels of pollution - and it should be banned.
It means that any child sitting in the back of a car while someone smokes breaths in high levels of smoke - which is really bad for them.
At moment, smoking in cars is not against the law in the UK.
But what do you think? Should smoking in cars be banned? Is it fair that passengers have to breath in other people's smoke?
If you send us a comment, it may be published on the Newsround website, and some comments may be used in our TV bulletins. We'll use your first name and your home town to show that it's your comment; your personal details won't be used for anything else.
"I think that it is a bad idea to smoke in cars because you and your children are breathing it in."
Daniel, Gloucestershire, England
"I think smoking in cars should be banned because not only are you putting yourself in risk but also other people around you."
Emily, Corby, England
"I think smoking in the car should be banned because the harm they do to their body they will also harm the children."
Hamid, Doncaster, England
"I think smoking in cars should be banned as not only can passengers breath in the smoke but they can get very ill or even die of passive smoking or they can get lung disease and it wont be their fault!"
Mollie, Kirkcaldy, Scotland
"I think smoking should be banned everywhere, but smoking in cars is very dangerous. The smoke could get trapped in the car if you don't have the windows down and the smoke could travel into someone outside, or someone inside."
Emma, Ballinamallard, Northern Ireland
"At our school we think that smoking should be banned in peoples cars because it's bad for children sitting in the back of the car."
Dylan, Kai and Kaylen, Middlesex, England
"No. It is bad for other people's health who are in the car. Also if the driver is smoking then they can get distracted."
Catherine, Glasgow, Scotland
"I don't think people should smoke in cars with a child."
Anna, Nottigham, England
"I think smoking should be banned because it will effect children's asthma and baby's could become ill."
Jodi, Stevenage, England
"I don't think that smoking should be banned because people should be sensible enough to not smoke when other people are in the car with them."
Natalie, Rutland, England
"I think that there should be a law against smoking in cars as not only can other people and even pets in the car breathe in the smoke. Also it can distract the driver which can potentially lead to an accident."
Mhairi, Inverclyde, Scotland