She told the Royal Commission into the Protection and Detention of Children in the Northern Territory that children had described feeling "angry, depressed and like a caged animal" and were too scared to complain about their treatment when she visited the centre last May.

"It was clear that use of isolation was routinely and frequently used and for very long periods of time, and when I say frequently and routinely I mean 23 hours a day for several weeks," she said.

"It was also clear that the use of force was routinely used as part of the everyday business of the facility, not just when there was an incident.

"I think all of those things are breaches of children's rights."

The royal commission follows revelations on the ABC's Four Corners program in July about the Don Dale centre that featured video footage of teenagers being tear-gassed and tortured.

The commission is being conducted by former Aboriginal and Torres Strait Islander Social Justice Commissioner Mick Gooda and former Queensland Supreme Court judge Margaret White, who were appointed to take over after the original commissioner, former NT chief justice Brian Martin, stepped down amid widespread criticism of his appointment from the Aboriginal community.

The commission reconvened on Tuesday and is taking evidence this week from bureaucrats, academics and health professionals.

In his opening address, senior counsel assisting Peter Callaghan said issues raised by Four Corners had been part of Australia's public life for years, but with little resolution.

He cited more than 50 reports that had relevance to issues covered by the royal commission's terms of reference.

"There was a national inquiry, there have been two royal commissions, four commissions or boards of inquiry, a parliamentary report, four Northern Territory government reviews and 23 independent reviews that have all published findings and recommendations that command our attention," he said.

"This commission is being held under the long shadow cast by the Royal Commission into Aboriginal Deaths in Custody."

Mr Callaghan said the 1998 royal commission findings in fact contained three specific references to juvenile detention: "The very fact that there have been so many reports prepared already raises, we suggest, another issue altogether. It invites a question: do we need to confront some kind of inquiry mentality where investigation is allowed as a substitute for action?"

Mr Callaghan said Aboriginal and Torres Strait Islanders were over-represented in NT youth justice and child protection systems. He said although they represented 30 per cent of the NT population, they accounted for 95 per cent of young people in detention in 2013-14 and 86 per cent of children under a care and protection order in 2014-15.

No sooner had Mr Callaghan finished his opening address than Andrew Harris, QC, told commissioners that the NT government was no longer funding former corrections minister John Elferink to pay for his legal representation throughout the hearings.

Mr Elferink was "relieved of his portfolio" the day after the Four Corners program on the Don Dale Detention Centre went to air in July.

"In its treatment of Mr Elferink, the ABC Four Corners program was dishonest and unprofessional," Mr Harris said, going on to explain he could not guarantee continuing to represent the broke ex-minister.

Sydney lawyer Peter O'Brien, representing Dylan Voller, the youth who appeared on the program wearing a spit hood and tied to a chair, asked permission for his client to be allowed to attend the commission public hearings or at least be allowed to watch them online in the adult prison to which he has been transferred.

"This has removed the description of these devices from the face of the legislation and provided now a discretion I understand, in the Minister for Corrections, to do anything they may need to do for the good order of the facility. This is quite problematic in terms of compliance with the kinds of standards that you'd expect," Ms Mitchell said.

Lawyer John Lawrence, representing Jake Roper, a 14-year-old inmate who was tear-gassed, put it to the Children's Commissioner that it was untenable to "put kids into a former adult prison" and asked how shackling a teenager to a chair and fitting him with handcuffs and a spit hood would be regarded by various international organisations.

"Its unacceptable in terms of children's rights and there are other ways of dealing with the situation," Ms Mitchell said.

Commissioner White expressed security concerns about the young prisoner attending the hearings and said watching proceedings online in jail was preferable.

A small protest was staged outside the Darwin Supreme Court before the royal commission began taking evidence. Local Aboriginal leader Kath Mills said it was the fourth royal commission and "nothing has changed".