Detaining children under the age of 14 is an "apprenticeship" to prison, an Indigenous rights advisor has warned, as calls mount to increase the age of criminal responsibility in the Northern Territory.

Key points: There are currently three children in detention in the NT under the age of 14

There are currently three children in detention in the NT under the age of 14 Just five young people are in supported bail accommodation across the Territory

Just five young people are in supported bail accommodation across the Territory The NT Government "in principle" backs lowering the age of criminal responsibility

The Royal Commission into the Protection and Detention of Children recommended raising the age of criminal responsibility from 10 to 12, and advised children under the age of 14 should not be detained except in the most serious of cases.

However, almost one year since the report was handed down, the recommendation is yet to be acted upon.

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The ABC can reveal there are currently three children who are under the age of 14 in detention in the Northern Territory — all of them aged 13.

Demonstrators descended on Darwin's Don Dale youth detention centre on Tuesday calling for change.

"We don't want a child with a criminal record when they're 14," said Rodney Dillon, an Indigenous rights advisor to Amnesty International.

"Where's a kid going to go that's been in a prison from when they were 10 to 14?

"We know where that kid's going to end up, that kid's going to end up in the prison system. That's the apprenticeship … it's the quicksand of justice."

There are a total of 44 people detained in the Northern Territory's youth detention centres, 13 of whom have been sentenced.

Territory-wide, just five young people are currently in supported bail accommodation — one of the Northern Territory Government's flagship reform strategies.

Rethink needed, health service says

"I think what we're doing at the moment is spending money in the wrong areas, in the wrong ways, and we need to rethink the approach," said Olga Havnen, CEO of Aboriginal health service Danila Dilba.

"I don't think there's any impediment for them to do it at any time to be honest, and to be frank, I think what's being done is a sort of minimalist approach."

There are currently three children in detention in the NT under the age of 14. ( ABC News: Tristan Hooft )

The sentiment was echoed by the NT Children's Commissioner, Colleen Gwynne, who said there was "no reason" why the Government could not implement the royal commission's recommendation.

The Government has repeatedly defended the pace of change in the youth justice system.

In a statement, Minister for Territory Families Dale Wakefield said a reform process was currently being worked through in cabinet.

"The Territory Labor Government has supported in principle the recommendation … that the age of criminal responsibility be raised from 10 to 12 years," she said.

"We are currently considering ways to implement this reform and will do so in a way that creates safer communities and also puts children at risk on the path to a better life."