A similar event happened here recently. A bookstore and the local branch of WWF (the environmental organization) invited schoolchildren and their parents to see a movie about environmental problems. The operator, an employee of the bookstore, plays the film from his/her* laptop. (*don't know the gender, sorry).
And the children were accidentally shown a porn movie. Apparently it plays for quite some time until some parents realize what had happened.
After the screening, a cheeky reporter asked one of the kids what the film was about. "Lady with gooey stuff on her face," the kid said.
Now that's another oops.