Supermarkets are being asked to stop displaying sweets, crisps and soft drinks at their checkout counters.
Sweets are often bought on impulse
Parents' representatives on the watchdog, the Food Commission, say it deliberately encourages children to pester them when they are queuing up to pay.
Up to 70% of sweets and snacks are bought on impulse, with many of these purchases being made at supermarket checkouts
where displays are placed strategically at a child's height.
The parents say this is manipulative marketing and are worried about the link between the consumption of high fat foods and growing levels of obesity.
Some supermarket chains are beginning to reduce targeting of children with confectionery and other unhealthy products at the checkout.
Waitrose and the Co-op have already banned sweets from checkouts. Tesco has snack-free paying areas in some stores.
Asda now says it plans to change its displays in the New Year.
Annie Seeley, a nutritionist and co-ordinator of the parents' panel, said: "Retailers know that putting snacks and soft drinks at the checkout where people queue increases sales substantially.
"But parents say this manipulative marketing technique leads to family conflict when children pester for the products and parents have to say no."
A survey by the parents' representatives found Asda had the largest volume of junk food on display at a typical till. Also in the bottom three were Safeway and Somerfield.
Waitrose was commended for not displaying sweets and junk food near tills. Tesco was second in the survey, having few snacks available at checkouts.
Safeway said: "Our policy is that generally we do not stock snack and sweets at the check-out.
"The main exception to this is at certain times of the year, for example Christmas, Easter and Mother's Day."