Dr Claire Achmad said government plans for a new Young Serious Offender category were not the answer to reducing youth crime, and would not build safer communities.
Under the planned law, a Youth Court judge will have the final say on declaring someone a Young Serious Offender.
A young person will be eligible if they are 14- to 17-years-old at the time of offending, have had two offences punishable by imprisonment of 10 years or more proven in court, and are assessed as being likely to reoffend, with previous interventions having proven unsuccessful.
The new category could see the most serious offenders in the age-group sent to military-style boot camps.
Dr Achmad said young people who offended have had lives of trauma, poverty and family breakdown - so it was the last thing they needed.
"It's going to be a label that's going to be hard for these children to move on from in their lives. So I want to see an approach that helps to rehabilitate these young people and help them on to a better pathway, rather than labelling them."
Achmad said young offenders needed to be held accountable for the harm caused but she was concerned that the creation of the new category would have "unnecessarily punitive impacts.... especially for our mokopuna Māori, mokopuna with FASD [foetal alcohol spectrum disorder] and other neuro-disabilities, and those who have been in our care and protection system.
"These are groups of mokopuna who are already overrepresented in the youth justice system."
Sunday's announcement included details of a military-style academy programme to be trialled from late July with children already in youth justice facilities.
Achmad said this had some positive aspects. They included "the promise of comprehensive assessment and bespoke plans, mentoring and transition support".
But, she added, from a children's rights perspective "nothing that is 'military style' should be used in the rehabilitation of our young people".
International and domestic evidence showed such approaches did not work in the long-term.
"Programmes that focus on positive prevention and early intervention - grounded in work led by iwi and community organisations - is what works and is already working in this context.
"I'd like to see the government scaling up these initiatives, which show that we don't need a 'military style' component to be included to make change."
A social investment approach would see a renewed focus on the causes of youth offending, Dr Achmad said.
A youth advocate said the government's moves were extreme and would not help the majority of at-risk children.
VOYCE Whakarongo Mai chief executive Tracie Shipton said they would not solve the type of youth offending the public was concerned about.
'With the extreme end of serious offenders the 10 young people proposed to go into the military-style academy you're talking about a maximum of 30 people and if you consider that that's not going to make a big change to what's happening on the streets of New Zealand."
Prime Minister Christopher Luxon said on Sunday during the announcement that New Zealanders were sick of crime and current approaches were not working.
"Let's try some things, let's have a different approach, let's do something different to try and get a different set of outcomes."
The government said the new approach aimed to reduce youth reoffending by 15 percent.
Minister for Children Karen Chhour said after the three-month residence stage, offenders would be helped for nine months with their transition back into the community.
"I actually see it as the biggest support network they'll probably ever have, actually putting the resources behind them, to enable them to be the best that they can be.
"These young people are smart, these young people have lost hope. And this is about giving them their hope back."
The pilot has been designed by Oranga Tamariki, police, the Defence Force, the Ministry of Justice, local mana whenua and other community groups.
