The Mothers' Union said 81% of mums and dads think the media encourages their children to ask their parents to buy them things that they see advertised.
A similar study in 2010 found that 39% of parents agreed that advertising is well regulated but in the latest survey only 30% agreed with the statement.
Head of Faith & Policy at The Mothers' Union and report author Lucinda Hasell said: "The subject of the commercialisation of children has received a lot of welcome attention in the last few years, but our research shows that parents are still concerned about this issue, and only half (51%) of those we spoke to felt equipped to manage the influence of advertising and the commercial world on their family.
"Further steps need to be taken to ensure that children are not exposed to inappropriate advertising and marketing and that parents are empowered to manage the impact of the commercial world.
"We are calling on politicians to ensure that this important issue remains a priority for the next government.
"Nearly half of parents we spoke to (45%) felt that advertising treated children as adults and 68% felt that advertising seen by children can be harmful to them.
"It is important that industry adheres not simply to the letter of existing regulation, but also considers how to meet the spirit of the regulation.
"Parents need to have support in both this way and also in the resources and information available to them, to ensure that the childhood of their children is valued by society as a whole."