Most parents, we can assume, would not let their four-year-old watch a movie about (to quote the Internet Movie Database) “a homicide detective … pushed to the brink of his moral and physical limits as he tangles with a ferociously skilled serial killer who specializes in torture and pain.”

But a family who traveled earlier this year on United Airlines say they found themselves and their kids subjected to the violent and sexually graphic film—and then subjected to questioning by security when they asked airline staff to turn off the movie.

James Fallows, a correspondent for the Atlantic magazine, recently wrote about the family, who contacted him about their experience on a United flight from Denver to Baltimore in early February. (Fallows declined to give their names.) According to the report, the in-flight movie shown that day was Alex Cross, which is rated PG-13 for “violence including disturbing images, sexual content, language, drug references, and nudity.”

The parents asked the flight attendants to turn off the drop-down screens above their family’s seats but were told that was not possible, Fallows reported. A flight attendant also said the screen could not be folded up, adding that that would prevent other passengers from seeing the movie. The family then asked if the captain had the authority to turn off the movie, but received no response. Ultimately, the parents focused on trying to distract their kids from the movie.

“Throughout these interactions the atmosphere was collegial, no voices were raised and no threats, implicit or explicit, of any kind were made,” the father told Fallows. An hour later, though, the captain announced that the flight was being diverted to Chicago for “security reasons.”

The security problem? The family. When the plane landed in Chicago, a police officer boarded the plane and asked the family to leave with her. At the gate, they were met by airline and airport officials as well as an FBI agent and other law enforcement officers. The family were questioned for a few minutes before being allowed to leave and get on another flight.

The Advocate contacted the airline’s media department about the incident but had received no response at deadline. In a statement to FoxNews.com, United said the flight had been diverted to Chicago “after the crew reported a disturbance involving a passenger,” adding, “We … have since conducted a full review of our inflight entertainment.”

In the Atlantic article, the father described the captain’s behavior as an “abuse of power” and expressed concern over what he called “United’s decision to inflict upon minors grossly inappropriate cinematic content, without parents or guardians having the ability to opt out. Had this been in a cinema or a restaurant, we would have simply left if the content were too violent, or too sexual, for a preschooler and a second grader. Cruising at 30,000 feet, leaving was not an option.”

The Boston-based Campaign for a Commercial-Free Childhood agrees. The nonprofit, which works to protect children from aggressive marketing, is asking supporters to write to United CEO Jeff Smisek asking that the airline stop showing PG-13 movies on overhead screens.

“For parents who travel with young children, being unable to escape from violent media is an all-too-familiar experience,” Susan Linn, CCFC’s director, said in a statement. “Flying with young children is a challenge in any case. But parents should be able to fly United or any airline knowing their children will be not be exposed to disturbingly violent images.”

The online petition, as well as more information, can be found at www.commercialfreechildhood.org/actions.