Unhealthy food makes a "startlingly" high number of appearances in children's television shows, researchers say.
Junk-food adverts are restricted during children's television in the UK.
However, a study, published in Archives of Disease in Childhood, found the shows themselves "skewed" towards unhealthy food.
The Children's Food Campaign said children were being bombarded with attractive images of unhealthy food.
Adverts for foods high in fat, salt and sugar aimed at children under 16 are not allowed in the UK.
A team of scientists at the University of Limerick, in Ireland, watched hours of children's television on the BBC and the Irish state-broadcaster RTE.
They found that 48% of food appearances were "unhealthy" such as sweets or chocolate while sugary drinks made up a quarter of all appearances of fluid.
Prof Clodagh O'Gorman, from the University of Limerick, told the BBC: "We were startled by how much food there was and surprised at the type of food consistently represented."
She said junk food was shown being consumed without consequence.
"Programmes have teenagers after school going to a coffee shop or fast-food outlet, having lots of sugary or high-fat foods and they're all thin and happy, and that's not realistic," she said.
"The foods which should be in eaten in moderation are eaten excessively on TV, and the staples, fruit and vegetables, are very infrequently represented."
However, the impact of the programming on the viewer is not clear cut.
Previous research has suggested a link between advertisements, children developing a "brand affinity" and wanting to consume that particular product.
"Our hypothesis is the children will want to eat fast food in general," Prof O'Gorman said.
Further research would be need to discover if that was true.
In the meantime, Prof O'Gorman called on parents, doctors and regulators to be more aware of the levels of junk food in children's television.
Malcolm Clark, the coordinator of the Children's Food Campaign, said: "It is disappointing that children's TV seems to be so tamely reflecting the obesogenic environment we all live in, rather than presenting a more positive vision of healthy, sustainable food.
"Children are bombarded with attractive images of unhealthy food and drink throughout their day - online, on billboards, in magazines, in shops, and still very much on TV.
"It is all part of the normalising of eating sugary snacks and sugary drinks that the food industry has so successfully achieved.
"We want the government to protect children by drawing up stricter rules, including switching off junk-food adverts on TV until after 21:00 and putting rules in place to stop children becoming fair game for internet marketing."
A BBC spokesperson said: "We broadcast lots of programmes to promote healthy eating to children and to help them understand where food comes from, with series like I Can Cook, Incredible Edibles and Blue Peter."