Researchers found that children aged five to 14 who take part in rugby league, cricket and Little Athletics are most at risk of ''excessive'' exposure to unhealthy messages through sponsorship by companies such as McDonald's and Coca-Cola Amatil.

Health experts say the saturation of fast-food and soft-drink promotion undermines the World Health Organisation's recommendation that the marketing of food high in saturated fat, sugar and salt be banned in children's settings.

''There is a fundamental conflict between sport and the promotion of sugary drinks,'' says Jane Martin, executive manager of the Obesity Policy Coalition.

''This is banned in other countries because they take the WHO recommendations seriously. If this continues we will have a generation of children that die younger than their parents.''

The study, published in the Journal of Science and Medicine in Sport, combined a survey of almost 3500 parents about the amount of time their children spent playing popular sports with a survey of food marketing in NSW junior clubs. It found 75 per cent of junior athletics, track and field and rugby league clubs, and 42 per cent of cricket clubs in NSW are sponsored by food and drink makers.

At those clubs, children are exposed to unhealthy food messages for two to four hours each week. In comparison, fast-food promotion was virtually absent at swimming, tennis and martial arts clubs.

Lead author Bridget Kelly, a lecturer in public health at Wollongong University, said the huge promotional opportunities companies have through branding on signage, uniforms, certificates and vouchers was far greater than any funding given to the clubs.

''It certainly wouldn't spell the end of junior sport if this was banned,'' Dr Kelly said. ''Multinationals like Subway and Domino's Pizza typically don't provide substantial amounts of money to the clubs, so they wouldn't fall apart if it was restricted.''

''Pervasive exposure'' in environments that are supposedly healthy was sending contradictory messages to nearly two-thirds of Australian children who participate in sport regularly, she said.

''We know children are influenced by the sponsors.''

With about a quarter of Australian children overweight or obese, Ms Martin said parents were struggling to protect their children from the junk food industry.

''If these companies were really serious about not promoting to children, they wouldn't be doing this. To see little children targeted by McDonald's is exploitation.''