Free giveaways like movie character toys have a powerful influence over what kids want to eat and can even make them more likely to choose healthier options, research from Cancer Council Victoria suggests.

The study involved almost 1,000 Australian children between five and nine years of age, who were offered a number of healthy and unhealthy meal choices after watching a movie trailer followed by a fast food advertisement or leisure activity.

Some of the meals came with a movie character toy and some did not.

Overall it found children were more likely to choose fast food. But the interest in healthy meals significantly increased when a toy was offered.

Lead author Helen Dixon from the Cancer Council said it proved what food companies have known for decades.

"When a movie character toy was offered with a fast food meal, kids were more likely to want that meal regardless of how healthy or unhealthy it was," Dr Dixon said.

"When you paired the toy with a healthy meal, kids were more likely to believe the meal looked better, they thought it would taste better and they'd feel more happy if their parents bought them that meal."

Jane Martin from the Obesity Policy Coalition said these powerful fast food promotions were so widespread it was very difficult to keep kids away from it.

"It's very, very hard to protect your kids from this kind of promotion, it's virtually impossible," she said.

"With one in four Australian kids currently overweight or obese, we should be supporting parents to make healthier choices, and not setting them up to battle with their kids over unhealthy food.

"I think that most children would not be requesting to go into a fast food franchise without the toy and the collectables."

Call for overhaul of standards

Ms Martin said toys and giveaways paired with junk food should be banned altogether and instead used to promote healthy options like fruit and vegetables.

"It shows that these kinds of promotions can be used in a way to harness children's interest and desires, and use it to put healthy food in front of them," she said.

Making healthy food fun and interesting is a great way to encourage kids, Jane Martin says. ( ABC News: Ian Cutmore )

Dr Dixon said advertising in Australia was regulated under a "complex" mix of laws and self-regulatory codes, which were inadequate.

"Leading groups like the World Health Organisation have expressed concerns about [the power of advertising] and urged people to restructure the food marketing environment so that it supports rather than undermines healthy choices for kids' diets," she said.

She suggested making companies satisfy nutrition criteria before they can conduct promotions.

"We know from analysis of advertising content on TV and other media that unhealthy food products like sweets, breakfast cereals, sugary junk food, snack food, fast food is very much overrepresented," she said.

"We know marketing works, companies wouldn't invest so much in it if they didn't think it worked."

'Government needs to protect our children'

Ms Martin said government needed to step in to regulate what kids were being exposed to.

"It is incumbent on the Government to act to protect children, industry is not doing a very good job at all, we shouldn't be relying on industry," she said.

"We have a serious problem on our hands with children's weight and diet, and I think we should be ensuring children are protected from these sorts of incentives attached to unhealthy foods."

Ms Martin said about 40 per cent of children's diets are made up of unhealthy food, and it can be difficult to reverse weight and obesity as adults.

But it was not all doom and gloom for parents, and encouraging kids to be involved in preparation went a long way.

"It's important to make healthy food fun," she said.

"You can make little shapes and faces out of food, get kids involved to chop it up and make it interesting. That's the message for parents."