Passive smoking leads to 17,000 children under five being admitted to UK hospitals every year, a local charity has said.
The Ulster Cancer Foundation has joined a global campaign to focus on the dangers to children when parents smoke.
"I love my smoke-free childhood," is an initiative promoted across the world by the International Union against Cancer.
The campaign is being launched on Monday, World Cancer Day, and will be a year-long effort.
Gerry McElwee, Head of Cancer Prevention, UCF, said four in 10 children in the United Kingdom grow up in smoking homes.
"A smoke-free childhood is crucial to nurturing a healthy start for children and reducing their risk of cancer," he said.
"Direct parental involvement is key to protecting the very young."
Mr McElwee said there was no safe level of exposure to second-hand smoke and even brief exposure could be harmful.
The core messages of the campaign are:
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