More than four in five (85 percent) of children don't have parental controls activated on their mobile phones, says the Carphone Warehouse.
Research by the mobile phone retailer, conducted by YouGov, revealed of those that haven't activated the control, 46 percent thought it wasn't necessary and 40 percent admitted they didn't know the function existed.
Furthermore, nearly half (48 percent) of parents believed it wasn't possible for children to download adult content on their handset, while just 21 percent said they know everything that their child does on their mobile phone.
"Online risks to children are as prevalent when they access the internet via their mobile phone as when they access it via their PC or laptop," said Professor Tanya Byron, the government's internet safety advisor.
"The recent influx of smartphones to the market means these are no longer just for business, but accessible to a much wider proportion of the market... including children. We need to apply everything that we've learnt through our research so far and make sure the same understanding, precautions and restrictions are applied to children using mobile phones to guarantee their online safety."
More than two thirds (68 percent) said children accessing adult content on their mobile phone is a growing problem and four in five (80 percent) of parents agreed they need more information and guidance to combat the threats created by technology
In a bid to offer parents with the advice they need, the Carphone Warehouse is offering a free booklet, which can be obtained through any of its 800 stores, in which Byron outlines the 'Talk, Act and Engage' strategy.
Byron said the strategy aims to encourage parents to communicate with their children, as well as employing features such as network filters and parental controls and even trying out the technologies themselves.
"We know how seriously parents take internet safety when it comes to the home computer. However, the idea of mobile web safety is still a relatively new concept for many," said Andrew Harrison, CEO of The Carphone Warehouse.
"Parents need to be savvy to children's usage in order to avoid possible dangers."
He added that the booklet's easy to follow tips will ensure "parents can be confident they're helping to keep their children safe while leaving them free to enjoy all the fantastic features of their mobile phone".