Parents often ignore age warnings on computer games and let their kids play 18-rated games, research shows.
Games which are rated 18 are often violent and scary but lots of parents still let their children play them.
"Most parents think their child is mature enough so that these games will not influence them," researcher Jurgen Freund told a games conference.
But a Nintendo spokesman said the games industry needed to look at ways to make parents more aware of games content.
All games get an age rating, in the same way as films do. This is done by the British Board of Film Classification (BBFC) and a European group called Pegi.
The research showed that many parents saw game ratings as a guide, rather than a ban on younger children playing them.
And putting an 18 rating on a game generally made kids want to play it even more, as they thought it would be cool and they liked the idea of playing something which they weren't supposed to.
However, the study also showed that not many games are actually 18-rated. Out of 1,208 games on sale between January 2003 and July 2004, just 16 of them had an 18 certificate.
Ways of making parents more aware of games ratings were talked about in a big meeting between the government, games makers and the BBFC in December, and it's hoped more talks will happen.