Pornography websites should have to carry out age checks before granting access, an industry regulator said.
Online video regulator Atvod, the Authority for Television on Demand, said laws should be changed to protect children from seeing adult material on the internet.
Research for Atvod found that 6% of children aged 15 or under had accessed an adult website over the course of a month, the BBC reported.
Some 5% of visitors to adult sites were under 18, and one website alone, Pornhub, was visited by 112,000 boys in the UK aged between 12 and 17.
The statistics were uncovered after the online habits of 45,000 desktop computers and laptop users were monitored over a month, with volunteers reflecting a cross-section of the population.
The issue of children accessing online pornography was so urgent that it was "critical the legislation is enacted during this Parliament", Atvod said.
It called for sites that did not comply with legislation to carry out age checks should be forbidden from processing payments from British customers.
Atvod already forces pornographic websites based in the UK to carry out age verification checks before customers can view explicit photographs or video, the BBC said, by requiring valid credit card details or personal information that can be checked.
But it said the vast majority of online pornography was downloaded from overseas businesses, over which it has no control.
Atvod wants all adults sites to request a licence that would only be granted if age checks were in place, with payment processors not allowed to handle fees for for services from UK citizens to unregistered sites.
Atvod chief executive Pete Johnson told the BBC: "We're a very substantial market and to access the money that's flowing from the UK would be quite a powerful incentive to introduce restrictions."
An Atvod spokesman added: "The material that appears on the free services is placed there by the paid services to attract customers to sign up to subscriptions.
"As long as the paid service placed content on a free service without age verification it would be in breach of its licensing conditions and so would not be able to access funds from the UK.
"We're not saying this will stop all children seeing all pornography online.
"But our argument is that even if you reduce the number of children who are accessing hardcore pornography online by 10%, that would be a significant win."