The political brawl over children in detention has reached a new low, with Greens senator Sarah Hanson-Young and Immigration Minister Peter Dutton trading personal insults over the case of a five-year-old girl set to be returned to Nauru from Darwin.

Mr Dutton on Thursday described statements by Senator Hanson-Young as "repugnant" after she accused the minister of "torturing" the girl, who has been diagnosed with post-traumatic stress disorder.

Greens senator Sarah Hanson-Young. Credit:James Alcock

Her PTSD is apparently the result of experiences inside the Australian-run detention centre. A report by Save the Children found she was displaying sexualised behaviour on Nauru.

Mental health experts have recommended the girl be housed in the community with her family but government officials have warned them they will be returned to Nauru.