Smoking should be banned in all cars, according to a leading group of doctors.
They say passive smoking still has a major impact on children's health with 22,000 across the UK needing treatment for things like asthma and wheezing.
Doctors say children are especially vulnerable to second-hand smoke in cars because it's so concentrated and need 300,000 extra GP appointments every year.
Matthew quit when his four-year-old daughter got asthma.
"We were going to the hospital and we told the doctor. She said it was the particles on her clothing that was the real effect for her asthma.
"That was when we realised it wasn't helping even smoking outside."
"We thought we were doing the right thing by going outside and smoking. We didn't want to smoke in the house with the kids because of the passive smoking.
"We thought going outside was eliminating it, but it wasn't."
The report from the Royal College of Physicians (RCP) calls for a total ban on lighting up in cars, as well as in open spaces like playgrounds and outside school gates.
Critics say it doesn't go too far enough though. Ministers don't have any plans to bring in a ban yet and are already carrying out a review of smoking laws in enclosed public spaces in England.
Professor John Briton is from the Royal College of Physicians and thinks a complete ban is needed.
He said: "Many parents believe that smoking in only one room or when the children have gone to bed will somehow protect the children from exposure. It doesn't."
The report found more than 20,000 chest infections, 120,000 bouts of middle ear disease and 200 cases of meningitis in youngsters are also thought to be linked to the effects of second-hand smoke both inside and outside the home.
Forty babies also die from sudden infant death syndrome every year caused by passive smoking, one in five of all cases.
Simon Clark, director of the smokers' lobby group Forest, says a ban isn't the right way forward.
He said: "If you ban smoking in cars, which is a private space, it's a small step to banning smoking in the home. Both measures are unacceptable and unenforceable."
A Department of Health spokeswoman said: "By increasing the level of awareness of the harmfulness of second-hand smoke, particularly to children, we will encourage people to voluntarily make their homes and private cars completely smoke-free."