Rates of obesity in children are on the increase in the UK
Junk food advertising makes it difficult to feed children a healthy diet, a consumer survey suggests.
Which? found 83% of those polled believed irresponsible marketing was making it harder to encourage children to eat well.
And most of the 2,000 questioned want the government to do more to control the marketing of unhealthy food to children.
But industry leaders said advertising in the UK is already heavily regulated.
A ban on adverts for junk food during television programmes aimed at children under 16 came into force in January.
However, campaigners had called for a complete ban before the 9pm watershed.
Which? said rules governing junk food advertising on the internet and on packaging were weak or non-existent, while current regulations on television advertising did not apply to the programmes most watched by children.
The poll of people over the age of 16 found 84% think there should be stronger controls on junk food advertising to children.
A bill to introduce robust restrictions on unhealthy food advertising to children, including setting a 9pm watershed, is due for its second reading in Parliament next week.
Clare Corbett, a food campaigner at Which?, said: "New types of promotions, like online and text messaging, have given food companies a whole new playground to promote unhealthy products to children.
"It's no wonder pester power is a continuing problem and our research shows the real strength of public feeling.
"With childhood obesity and diet-related health problems on the increase, the government must take serious action and soon."
But the Food and Drink Federation said it did not recognise the picture painted by Which?
Julian Hunt, FDF director of communications, said: "When it comes to the marketing of food and drink products, the UK is now one of the most heavily regulated countries in Europe.
"Our members take a responsible approach to the way they market their products and further restrictions would seem to be neither necessary nor proportionate."
Baroness Peta Buscombe, chief executive of the Advertising Association, said a recent Ipsos Mori poll found that 76% of UK adults believe that introducing a 9pm watershed on food advertising would not reduce the level of childhood obesity.
"The reality is that the advertising industry takes a very responsible approach to food advertising.
"There has been a real change in the nature and balance of food advertising to children."