Sex, violence and swearing has increased significantly in US movies over the past decade, a study suggests.
Researchers found there had been an increase in sexual content
Ratings have also become more lenient during the period, according to a study by Harvard University.
Researchers suggested that the "ratings creep" indicted the Motion Picture Association of America was relaxing ratings standards.
They called for improvements to the current US system that rates new films for suitability.
The research carried out by the Kids Risk Project at the Harvard School of Public Health found that films rated parental guidance (PG) and parental guidance for
children under 13 (PG-13) had become more violent between 1992 and 2003.
They also concluded there was also more sexual content in films rated PG, PG-13, and R, which requires children under 17 to be accompanied by an adult.
Kimberly Thompson, from the Kids Risk Project, said: "It's time for a significant research effort to explore the development and creation of a universal media rating
Animated films rated G - for family viewing - were also found to contain more violence than non-animated films with the same rating.
The study concluded: "Parents must recognise their responsibility in choosing
appropriate films with and for their children, and in discussing the messages in films with children to mediate any potential adverse effects and reinforce any potential