Food giants should be forced to include pop-up health warnings on websites that carry "addictive" games targeted at children, councils have said.
Online "advergames" are plugging foods containing high levels of sugar, salt and fat, said the Local Government Association (LGA), which represents almost 400 councils in England and Wales.
It believes the games - which can be easily accessed on computers, tablets and smartphones - are undermining "decades of hard work by health bodies to tackle obesity".
Alongside pop-up warnings, the LGA wants tighter advertising rules on what can be marketed to children.
Top brands including Chewits, Nesquik from Nestle, and Sugar Puffs all offer games on their websites.
Katie Hall, chair of the LGA's community well-being board, said: "It is unacceptable for food giants to be targeting children with these addictive games.
"Food manufacturers are weaning youngsters on to a diet laden with sugar, fat and salt - creating the next generation of unhealthy children.
"This can have long-term consequences which can last into adulthood. Councils are already being forced to tackle the obesity epidemic with shrinking resources.
"Latest research shows over a quarter of infants aged three to four now use a tablet computer at home, which is why this issue needs to be addressed."
Ms Hall said health warnings was the only way of "tackling this issue head-on".
She added: "We cannot allow firms to promote obesity through the back door and help fuel the country's epidemic."
Figures published yesterday in the Chief Medical Officer's annual report show that 77% of parents of overweight children do not recognise that their child is heavier than they should be.
Between 2006/07 and 2012/13, some 27,860 children every year were also found to be severely obese - on or above the 99.6th centile for weight, the study for Professor Dame Sally Davies said.
A December 2012 report for the Family and Parenting Institute, co-authored by Dr Haiming Hang from the University of Bath, found that even children as old as 15 did not recognise that advergames were adverts.
It said "advergames persuade on a subconscious, emotional level" and can directly impact on a child's behaviour without them being aware of it.
Furthermore, the study found that advergames were widely used for products high in salt, sugar and fat.
It said: "These products are banned around children's TV programmes so advergames exploit a regulatory loophole", adding that voluntary codes around the games had proved "ineffective".
A spokeswoman for the Advertising Standards Authority (ASA) said: "Advergames by food companies have to stick to strict rules.
"We've banned advergames that promoted overeating and will not hesitate to ban any others that encourage unhealthy diets or lifestyles.
"We've also issued clear guidance to advertisers to help them prepare their advergames responsibly.
"On top of this, we've just announced that we're conducting new research and monitoring the sector to ensure that the regulation of food and soft drink advertising continues to be effective and proportionate, particularly when it comes to protecting children online."
The LGA warning comes after a report from the British Heart Foundation (BHF) last week found that youngsters who stay up and watch prime-time TV are being "saturated" with junk food ads.
Those who watch television between 8pm and 9pm can see as many as 11 junk food adverts an hour, according to analysis of more than 750 adverts.
More than one in 10 (13%) of the food ads were for fast food chains and 12% were for chocolate and sweet companies.