The Government has launched an advertising campaign on the "hidden dangers" of second-hand smoke to young children.
New TV and radio adverts in England will show that smoking by a window or the back door does not protect youngsters from harmful effects.
According to figures from the Royal College of Physicians, millions of children in the UK are exposed to second-hand smoke that puts them at increased risk of lung disease, meningitis and cot death.
Second-hand smoking results in over 300,000 GP visits among children ever year, 9,500 hospital visits and costs the NHS more than £23.6m annually.
A survey of 1,000 children aged eight to 13 whose parents are smokers was released to support the campaign.
It found 98% wished their parents would stop smoking, 82% wished their parents would not smoke in front of them at home and 78% wished they would not smoke in the car.
Meanwhile, 41% said cigarette smoke made them feel ill while 42% said it made them cough.
Health Secretary Andrew Lansley said: "We all know smoking kills but not enough people realise the serious effect that second-hand smoke can have on the health of others, particularly children.
"This campaign will raise awareness of this danger and encourage people to take action to protect others from second-hand smoke.
"This is just one part of our wider strategy on tobacco. We need to do more.
"That is why next week we will end tobacco displays in large shops. We will also be consulting on plain packaging this spring."
Dr Charles Godden, consultant paediatrician at the Royal Surrey Hospital, said: "I see children every week with conditions which are made worse by second-hand smoke.
"Most parents would be horrified to know that even a short car journey where an adult has been smoking would result in breakdown products of nicotine in their child's urine.
"This shows exactly why we should all make our homes and cars smoke-free and that children need protection from exposure to second-hand smoke."
Professor Terence Stephenson, president of the Royal College of Paediatrics and Child Health, said: "Levels of tobacco smoke in a car can be even higher than in a smoky bar and second-hand smoke has been strongly linked to chest infections in children, asthma, ear problems and cot deaths.
"We have long campaigned on this issue and today's announcement is a significant victory.
"But when it comes to smoking in cars when children are present, we are calling on Government to now go the extra mile and make it illegal."
Emily Humphreys, head of policy and public affairs at Asthma UK, said: "Research has found that children whose parents smoke are 1.5 times as likely to develop asthma as those whose parents do not smoke.
"Additionally, children living with parents who smoke have higher chances of later taking up the habit themselves."
Simon Clark, director of Forest smokers' group, said: "Yet again smokers are hit by a fusillade of estimates and calculations designed to spread fear and revulsion.
"It's only a matter of time before loving parents who smoke in or around their homes are accused of child abuse and risk having their children taken into care.
"Tobacco is a legal product. Adults must be allowed to smoke somewhere."
A campaign against smoking in cars was launched in Wales in February.
The Welsh Government's "Fresh Start Wales" campaign included advertising on local radio, billboards, bus-backs and bus shelters as well as a dedicated website, www.freshstartwales.co.uk.
And in July last year, Welsh First Minister Carwyn Jones said his Government would consider pursuing a ban on smoking in cars carrying children if youngsters' exposure to second-hand smoke in vehicles did not start to fall within three years.
He said at the time: "Wales was the first UK country to vote in favour of a ban on smoking in public places and if necessary we will not shy away from considering legislation to further protect children from second-hand smoke."