A government advert aimed at convincing parents to give up smoking upset children and broke several rules, the Advertising Standards Authority says.
The independent regulator ruled that the "I'm not scared" TV advert, which attracted 51 complaints overall, should not be shown before 7.30pm.
In it, a girl says she is not afraid of spiders, clowns or bullies, but does fear her mother - a smoker - dying.
The government said it proved effective at making adults consider giving up.
About half of those who complained said the advert, which was launched at the end of October, had distressed their children.
There were an additional 13 complaints about the radio version, which featured the same child's voice.
The decision comes as the ASA said a Volkswagen TV advert showing an engineer fighting with replicas of himself was shocking, offensive and unsuitable for children.
Listening alone
The ASA said it recognised the "serious and worthwhile" nature of an advert designed to make parents consider the emotional impact of smoking on their children.
The 'Scared' campaign was very effective at targeting our core, harder to reach, smoking audience - NHS smoking services were contacted by three times more people than expected
But "we considered that hearing an otherwise fearless peer say she was scared her mum might die because she smoked could frighten and distress young children, particularly if they had misunderstood that the risk of death was imminent.
"We considered that the ad could cause distress to children if they were watching TV alone, without their parents or family to explain the ad to them.
"We recognised the importance of the ad reaching its target audience - adult smokers who were parents. But we judged it necessary to balance targeting that audience with avoiding distress to young children."
It ruled the advert had therefore breached four child-related regulations and should not be broadcast before 7.30pm, when any child watching TV was likely to be in the company of his or her parents.
But it did not uphold any complaints about the radio advert, judging that any child listening would likely be in the company of family - over breakfast or during the school run in the car.
A spokesperson for the Department of Health said: "Our advertising is not meant to shock but to make adult smokers think about their smoking behaviour and the effect it has on their loved ones.
"The 'Scared' campaign was very effective at targeting our core, harder to reach, smoking audience - NHS smoking services were contacted by three times more people than expected."
While numbers are dropping, more than a fifth of UK adults still smoke.
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