Mr Harmer said officers on a power trip regularly swore at kids, calling them "oxygen thieves", "camp dogs" and racial slurs like "black poofter".
Guards screened graphically violent movies, including ‘Grand Theft Auto’ for the kids, many of whom were in detention for stealing cars.
Girl inmates who couldn't keep sanitary items in their cells were too embarrassed to ask male staff for tampons.
"Deliriously tired" staff sometimes fell asleep on the job, after being forced to do back to back double shifts, which were physically and emotionally exhausting.
Some 95 per cent of inmates were Indigenous, yet there was supremely limited cultural competence training for the mostly white guards, and the Elders visiting program rarely occurred.
"We had an Aboriginal, not a full blood Aboriginal but a half caste person, come in and conduct an awareness program... for one day," Mr Harmer said.
Former guard Eliza Tobin recalled a pregnant girl from a remote Indigenous community who was doing time for murder and barely spoke English.
"She was thrown in the mix with all these Darwin urban girls who don't speak any language... whereas this girl had come from hunting, fishing, gathering... it was, with me being white, difficult," Ms Tobin said.