Instances in which police officers capsicum-sprayed a handcuffed child and did nothing to stop a girl hitting her head against a cell door more than 200 times have been revealed as the most serious sustained complaints against Northern Territory Police over the past year.

The Royal Commission into the Protection and Detention of Children in the NT has been holding hearings all year to examine the treatment of young people by corrections staff and police, following the tear-gassing of six teens at Darwin's Don Dale Youth Detention Centre in 2014.

But the NT Police Commissioner denied that his officers had a problem managing youth.

"We deal with thousands of youths per year and the majority of police do the right thing. We do have some officers who need managerial guidance or, if it's more serious, we take disciplinary action," Commissioner Reece Kershaw said.

'Skinny, small' child gassed by police while cuffed in cage

Ombudsman Peter Shoyer found that the capsicum spraying of a "skinny, quite small" boy aged 11 while he was handcuffed and contained in the cage of a police van was inappropriate and risky.

The boy, who had been sniffing a volatile substance, was spit-hooded and handcuffed after repeatedly spitting at officers, and tried to use the hood to choke himself, before pulling it off. Officers told him if he spat at them again he would get sprayed; the boy then spat on one officer and was sprayed.

"During the period in the van after discharge of the spray, the child was displaying extreme distress and yelling and crying constantly," Mr Shoyer said.

He found that police had failed to properly communicate with the child before the spraying, and that there were several other options they should have considered.

"Further efforts could have been made to engage the child in genuine conversation, explaining what was happening and then seeking his co-operation; this may or may not have worked," Mr Shoyer said.

"The fact that the spray was being discharged in a small, confined space… would almost certainly make the situation worse."

NT Police Commissioner Reece Kershaw says most officers do the right thing. ( ABC News: Felicity James )

Police must remember they're dealing with children: Ombudsman

The head of the Operational Safety division of NT Police said the use of the spray by four officers on a handcuffed child in the closed cage of the van did not appear to him to be a "reasonable response".

"There was no direct threat to any person at the time the [spray] was discharged," the Ombudsman reported him as saying.

"While assault by spitting is generally considered by the standards of the community to be disgusting and provocative, provocation is no excuse for the application of force after the fact."

He found there were no extraordinary circumstances to justify the use of the spray on a child who was cuffed or secured, in line with police protocols, but his views were dismissed by NT Police's internal investigator, who also questioned whether an 11-year-old is a young child.

"I do not doubt for a second [that they are]… It is important that officers not lose sight of the fact that they are dealing with children," Mr Shoyer said.

"Their circumstances may differ appreciably from adults and there will frequently be times when a different approach is required to meet those circumstances."

Police must remember that they're dealing with children, the Ombudsman says. ( ABC News: Xavier La Canna )

Police did not stop girl hitting her head more than 200 times

In a second serious incident, Mr Shoyer upheld a complaint against police after it was found that several officers did nothing after witnessing an intoxicated 16-year-old girl hitting her head against a cell door.

"A number of officers saw what she was doing but there was no move to attempt to stop or dissuade her from hitting her head until after officers were contacted by a Duty Superintendent and told to take action," Mr Shoyer said.

"It is clear the Custody Sergeant made a conscious decision not to act in the face of the complainant hitting her head against the door… a Custody Nurse on duty at that time also stated that the complainant wasn't hitting her head 'that hard'," he said.

He said that in CCTV footage of the incident it was evident that on some occasions the girl "was exerting considerable force" in hitting her head.

"The risk that the complainant might do some damage in over 200 instances was real and should have been addressed much earlier than it was," he said.

'Use of force is our last option': Commissioner

The NT Government says it's trying to keep kids away from the justice system altogether. ( ABC News: Eleni Roussos )

"In the whole our police force is treating young people very, very well, and we have very strong processes and systems in place to ensure that there's accountability and transparency when it comes to [dealing with] young people," Commissioner Kershaw said.

"Our preference is to resolve the matter without any use of force at all… that's what we teach our officers.

"We like to try to communicate, contain, and even if we've got to reverse out of that situation, we will."

Chief Minister Michael Gunner said his Government was trying to divert youth away from the justice system.

"We don't want to see pepper spray used on an 11-year-old. I think we can all agree with that. that's not an ideal outcome in any way, shape or form," he said.

"When you look at our policies about investing in children, in the youth justice cycles, how can we actually get intervention earlier so police are simply not having to deal with youth?"