The system by which video games are rated in the UK is to be made "simpler and stronger", the government has said.
Games will now be rated by the Video Standards Council (VSC) in line with Europe-wide guidelines.
Previously, additional ratings were decided upon by the British Board of Film Classification (BBFC).
The new system means for the first time that anybody selling a 12-rated game to a child under that age could face jail.
The Pan European Game Information system (Pegi) gives games an age rating as well as additional information such as violent content and bad language.
The VSC will now rate games to Pegi's specifications while enforcing compliance among retailers.
The new ratings do not apply to games bought online.
Creative Industries Minister Ed Vaizey said: "It will give parents greater confidence that their children can only get suitable games while we are creating a simpler system for industry having their games age-rated."
While the BBFC will now largely stop assessing content in games, it will still be called upon to judge games with gross violence or sexual material.
Games and entertainment body Ukie said the new system provides "much needed clarity for consumers".
"We are also in the planning stages of a major awareness campaign to help the public understand the system and other aspects of responsible gaming as soon as Pegi become law in the UK," Ukie chief executive Jo Twist said.
Richard Wilson, from UK games industry trade association Tiga, said the changes were a necessary "evolutionary" step.
"It simplifies the system," he told the BBC.
"The Pegi system is reasonably easy to understand.
"The fact there are criminal sanctions in place will mean that retailers will want to train and support their staff."
The new system is expected to come into force by July this year.