Over a third of parents say their children have suffered sunburn, a survey reveals.
The campaign kicks off this week
The poll also reveals that 41% like to see their children with a tan.
Cancer Research UK ,which commissioned the survey, said the findings showed many parents were failing to take skin cancer warnings seriously.
The findings were published to mark a new public awareness campaign, which will see posters in nurseries, GP surgeries and outlets of Boots.
The poster, created for Cancer Research UK's SunSmart campaign, has been designed to highlight how quickly children's skin can burn in the sun.
It features the slogan "Kids Cook Quick" along with a picture of two sunburnt children sitting on the beach. Some 19,000 posters will be distributed across the UK.
"This poster has been created to help remind parents to protect their children," said campaign coordinator Sara Hiom.
"Our survey shows that just over three-quarters of parents know that it's never OK for a child to go red in the sun, but they may not always realise that young skin can burn very quickly, in as little as 10 minutes.
"Sometimes, even with the best intentions, we can be caught out.
"We hope the Kids Cook Quick slogan will stick in parents' minds over the summer and remind them to make sure their children are properly protected whenever they are in the sun, by following the SunSmart code.
"This means seeking shade in the middle of the day, covering up with a hat, t-shirt and sunglasses, as well as using sunscreen that is factor 15 or higher."
Dr Catherine Harwood, consultant dermatologist for Cancer Research UK, urged parents to cover children up when they are in the sun.
"As children have much more opportunity to play and take part in sports and other outdoor activities, they spend far more time in the sun than adults.
"Babies' and toddlers' skin is particularly susceptible as their skin is thinner and produces less protective pigment.
"We get around 80% of our exposure to the sun before the age of 21. So it is vital that parents are aware of the dangers and know how to protect their children properly."
The British Skin Foundation urged Britons to cover up during the summer.
"We must take care of ourselves by covering up and using sunscreen with an SPF15 or above and SPF30 for children, especially on the triangle area between the nose, chin and ears where most tumours are found," said Dr Colin Holden, its spokesman.