There has been an outcry in Britain over firms that use paid ''mini-marketeers'' to push products to their peers in the playground or on social-networking sites.

Australian authorities have focused on restricting junk food ads during children's television programs, but digital advertising to young people is not strongly regulated.

A founding member of the Coalition on Food Advertising to Children, Kaye Mehta, describes digital peer-to-peer marketing as potentially a bigger problem than television advertising.

''Marketing has been going on for a long time but it's getting more and more aggressive and more and more sophisticated,'' she said.

''Marketers are using children through the alpha peer process to promote products and influence other children. Social media sites make this very easy to do.

''If we thought that the traditional form of marketing through the TV was bad, well marketing in the digital media is even more sophisticated and allows marketers more innovative techniques to get to children.

''The process of viral marketing and children promoting products to other children, it's clever but it's insidious.''

Manager of lobby group the Parents Jury, Karen Sims, said the lack of regulation on digital advertising and children is cause for alarm.

''In the digital age, advertising exists everywhere,'' she said.

''Viral marketing is particularly insidious. You have children marketing to other children on social networking sites. It is relentless, it is not well regulated and it is very hard for parents to monitor.''

Ninety-one per cent of children between the age of six and 10 believe a product is cool because their best friend does, according to a 2010 study commissioned for British magazine Marketing Week.

Globally, the ''tween'' market of children aged between six and 13 spends an estimated $328 billion of their own money and influence another $2 trillion of parental spending each year.

Ms Mehta, a dietician-nutritionist at Flinders University, said children's exposure to unhealthy food messages was increasing, within a context of high levels of childhood obesity.

She has researched how food and beverage companies use social-networking sites to get to children.

''It's cheap to reach children through social-networking sites,'' she said.

''In terms of market research, they get feedback on their products, they can ask children to suggest new flavours and new products.

''Children think it's fun and engaging but they are being used. They are being used to do the work of corporations and make corporations profits.''

Sites such as Facebook, Twitter and Bebo have an age restriction of 13 while you have to be 14 or older to have a MySpace account.

However, market researchers can conduct surveys with children aged as young as eight, provided they have parental consent and follow a stringent code of conduct.

Australian Market and Social Research Society president Peter Harris said snack food was one of the most commonly researched products with children.

''A lot of the food companies in Australia use market research to do taste testing, product development and packaging innovations with children,'' he said. ''However, they tend to steer away from using children to test unhealthy foods.''

Sharyn Smith, the chief executive of Australia's largest word-of-mouth agency, Soup, said it was unethical for marketers to recruit young children for campaigns.

Soup does not recruit anyone younger than 16, she said.

''Word-of-mouth at the end of the day is about the authenticity of someone genuinely believing in the product,'' she said.

''We certainly stay on the side of genuine, authentic recommendation … paying children to provide positive word-of-mouth is just wrong.''

She has been alarmed to see an increase in companies paying people to post positive product reviews on Twitter.

''It undermines trust and ultimately undermines confidence in the brand,'' she said.

A spokesman for regulatory body, the Australian Communications and Media Authority, said it monitors television advertising but was not looking at digital advertising.