Governments must do more to protect children from food marketing in the fight against obesity, an expert says.
15% of 15-year-olds are obese in the UK
Professor Philip James, chairman of the International Obesity Task Force, will tell an Italy conference it is time for governments to get tough on regulation.
He is expected to say children are increasingly exposed to not just ads, but also sophisticated marketing techniques such as text messaging.
The food industry said firms were taking a more responsible approach.
But a report, published by the consumers' association, Which?, said "underhand marketing tricks" were being used to target children.
The study cited examples of internet promotions, toys and computer games and "misleading" health claims being used.
Worldwide, more than 22m children under five are seriously overweight, with rates rapidly increasing in much of the developed world, especially Japan and the US.
In the UK, 15% of 15-year-olds are classed as obese, but that is expected to rise to a quarter by 2020.
Companies have long been criticised for promoting unhealthy food and drinks to children.
Tory leader David Cameron recently attacked WH Smith for promoting half-price Chocolate Oranges at its check-outs instead of real oranges.
And a survey of more than 2,000 items at nine supermarket chains found none met the target of offering a third of promotions on fruit and vegetables.
In the UK, the government has proposed banning junk food TV advertising at times when children are watching and introducing clearer labelling on foods.
But in a speech to the Hormones, Nutrition and Physical Performance Conference in Turin on Monday, Professor James will say that just touches the surface.
He is expected to say just a small proportion of marketing budgets goes on TV advertising, with firms resorting to more sophisticated techniques such as mobile phone messages and placing products in stores where children are likely to see them, such as at check-outs.
There have been huge changes in society, such as more mothers working and more time spent inside, which have meant children are more susceptible to marketing, he will tell delegates.
He will say this means children are being exposed to "intense food industry marketing at an age before their brains can distinguish parental advice from advertising".
And while families need to change their dietary habits, Professor James will add government action through regulation is "crucial for protecting children".
"The societal pressures on children to consume food which has little nutritional value is extreme.
"There needs to be far greater commitment by governments to protect children.
"It's very questionable whether the lives of children should be commercialised in the way they are - this is only a phenomenon of the last 20 years, and it's contrary to every civilisation's understanding of how to nurture children."
But a spokesman for the Food and Drink Federation said the industry had reformed its ways in recent years.
"We realise firms need to be responsible, that is why we have cut salt content, started to introduce better labelling and looking at advertising."
And a Department of Health spokeswoman agreed the promotion of unhealthy food to children was a concern, but steps were being taken through the ad ban and food labelling proposals.