The report, by the AA's Food Advertising Unit, shows significant change in food and soft drink advertising and promotions ahead of the Government's interim review.
It shows that there has been a downward trend in exposure by children to food advertising between 2003 and 2006, even before Ofcom's new rules were introduced earlier this year.
The new rules on junk food advertising to children banned foods high in fat, salt or sugar being shown during or around programmes that are made for, or could appeal to, children under 10.
Between 2003 and 2006 ad spend on confectionery, potato crisps and snacks, full sugar carbonates, breakfast cereals and fast food restaurants fell by almost 9% or £26m across all media.
In the first seven weeks since the new restrictions came into force, the number of ads for such products watched by 4- to 9-year-olds on TV declined by almost a third compared to the same period in 2006. As the new restrictions are further implemented for under 16s in January 2008 there will be further considerable change.
The report also revealed that Food Standards Authority and Ofcom research shows that advertising only has a modest effect on children's food preferences. The research suggests that the obesity problem will only be successfully addressed by a holistic and wide-ranging approach, not by further advertising bans or restrictions.
The report concludes that a pre-9pm watershed band would be "a blunt instrument that would be disproportionate and unnecessary, given the new restrictions in place".
Baroness Peta Buscombe, chief executive of the Advertising Association, said: "This report shows the progress already made by the responsible food and soft drink advertising industry which has taken steps even before the introduction of the new rules to change the nature and balance of advertising and promotions.
"We hope the Government will see this as a positive signal when it conducts an interim review this autumn."