Both men were detained by a school security officer after they were found walking the hallways while school was in session the afternoon of March 25, Old Tappan Police Chief Joseph Tracy said.
Students they knew had let the pair into the building through a side door, the chief said.
The school went into a shelter-in-place as a precaution, with students and staff brought to the football field while Bergen County Sheriff's K-9 Units scoured the building, Tracy said.
Students were dismissed from there, parents said.
The exchange students, meanwhile, were taken into custody and brought to police headquarters for processing, the chief said.
Parents said they believed the students who let them in were girls who'd met the Frenchmen during a mission trip to Africa last summer. School officials were expected to deal with them.
Click here to follow Daily Voice Bergenfield and receive free news updates.