Asda, Morrisons and Iceland have been named as the "worst offenders" for undermining parents' efforts to feed their children healthily.
The Children's Food Campaign (CFC) said the three supermarkets displayed unhealthy food or drink at more than 80% of their checkouts.
It also criticised the Co-operative, Sainsbury's, Tesco and Waitrose for making families queue past displays of unhealthy snacks to reach the tills.
Not one "traditional format" supermarket in the survey had any healthy food options promoted at its checkouts, the report said.
The Checkouts Checked Out report found that most supermarket branches and high street stores routinely promote unhealthy snacks at their tills and in their queuing areas, despite several promising to reduce the practice.
The survey of stores across London found that, in many cases, junk food such as sweets and crisps was positioned at children's eye level.
The trend had also spread to smaller stores and non-food retailers including HMV, New Look, Superdrug and WHSmith, which all displayed sweets and chocolates in the queuing area near the checkouts, the CFC said.
A questionnaire to each of the retailers found that just one, Sainsbury's, confirmed a policy of not selling "impulse confectionery" at their main checkouts, but added that they did display "gifting confectionery or seasonal lines".
The campaign did commend the Waitrose store in Oxford Circus for its prominent display of fresh fruit in the queuing area before the tills, and called for this to be the norm across all stores.
CFC spokeswoman and co-author of the report Sophie Durham said: "Impulse purchases at the checkout can add several hundred unplanned calories to a family shopping basket.
"Supermarkets claim to be responsible retailers, yet they continue to put their profits ahead of families' health. They should stop prompting pester power and help parents by removing promotions of sugary, fatty, salty and calorie-laden snacks and drinks near the checkouts, especially those placed within easy reach of children.
"It's time to get the junk off the checkouts once and for all."
Annie Seeley, a nutritionist and co-ordinator of the Food Commission's Parents' Jury, which investigated snacks at the checkout between 2002 and 2005, said: "I am disappointed but not surprised that parents need to campaign again on this issue.
"Supermarkets seem to have reneged on their promises made after the Food Commission's investigation a decade ago and returned to the same bad old marketing habits of selling snacks high in sugar, salt and fat at their checkouts."
The CFC has launched a campaign supporting parents to lobby supermarkets to stop promoting unhealthy food to children.
It is also lobbying the Advertising Standards Authority to regulate all promotion of unhealthy food to children alongside broadcast and print advertising.
Asda said: "We thank the Children's Food Campaign for this report. We sell a wide range of products on our checkouts from batteries to bags for life."
A Waitrose spokeswoman said: "Research carried out last year with our customers told us that they would like greater visibility of our seasonal ranges.
"As a result we have introduced checkout displays which are designed to highlight some of our seasonal and new products, including food and non-food items.
"Recently featured items have included healthy products from our new 'LOVE life you count' calorie-controlled range, as well as seasonal confectionery."
A spokeswoman for the Co-operative Group said: "The sale of all products that are high in fat, sugar and salt (HFSS) from fixtures on checkouts and kiosks is prohibited in all our stores. Sugar-free gum/mints and medicated sweets are permitted.
"However, many of our stores are small convenience stores, which limits what we can do in terms of siting HFSS products elsewhere in store.
"Nonetheless, we are committed to avoiding direct marketing and advertising to children of HFSS products and, over a decade ago, we removed all children's characters from own-brand packaging classed as HFSS, with the exception of seasonal and special occasion products."
Andrew Opie, food director of the British Retail Consortium, added: "Retailers are doing a great deal to promote healthy eating in their stores. This includes selling healthier snacks, promoting fruit and vegetables and even reformulating products to reduce the calories and salt they contain.
"Focusing on how products are sold in one part of some stores ignores the bigger, positive picture.
"Retailers exist to offer value and convenience to their customers. There's a whole range of products to be found near check-outs, including batteries, magazines and gift cards."
Netmums founder Siobhan Freegard said: "In the last 10 years we have made so much headway in the battle against junk food with clearer on-pack labelling, Ofcom regulations on what kinds of food can be advertised to children and transparency over additives, but when it comes to the simple issues of junk food on display by the checkout we are back to where we started 10 years ago.
"Stores must stop working against mums and dads and work with us."
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