One R-rated movie, 'Scary Movie', was seen by an estimated 10 million children, or about 48 percent of 10-14 year olds.
"Our data reveal a disturbingly high rate of exposure among 10-14 year olds nationally to extremely violent movies," said Keilah Worth, the lead author on the study and a post-doctoral fellow at Dartmouth Medical School and at Dartmouth-Hitchcock Medical Center's Norris Cotton Cancer Center.
"In Britain, no adolescent would be admitted to these movies unless they were 18. The R rating in this country is clearly not preventing our young people from seeing them," Worth added.
For the assessment of exposure to violence in movies, the researchers used data from national telephone surveys of more than 6,500 adolescents age 10-14 in 2003.
Out of 532 recent releases, the researchers chose to look at exposure to 40 of the most violent movies.
The study also revealed some independent risk factors for exposure: boys, minorities, those with lower socio-economic status, and those with lower academic performance were all more likely to see extremely violent movies.
Black male adolescents were at particularly high risk of seeing these movies.
"No expert in child development would advocate for subjecting children as young as 10 to this level of violence, yet the study shows that such exposure is commonplace in this country," said James Sargent, the senior scientist on this study and a professor of paediatrics at Dartmouth Medical School.
"We should re-think the current movie rating system, which has been in place for 40 years, and was designed when kids could only see movies in theatres.
"Ratings need to be more prominent on all movies, whether they are seen in theatres or purchased in the store, and we need clearer messages to parents.
"Paediatricians and child advocates should instruct parents to strictly abide by the movie-age guidelines and to closely monitor movie viewing," he added.
The study is published in the August issue of the journal Paediatrics.