A second 15-year-old was held at a police station for five nights last week due to an ongoing shortage of youth residential beds.
The Hawkes Bay teenager was charged with breaching his supervision order and had a history of failing to appear in court.
He was only supposed to spend one night in the Hastings Central Police Station before being moved to an Oranga Tamariki residential housing facility.
But when a bed could not be found, he was forced to stay for a further four nights.
Yesterday RNZ reported another 15-year-old boy was held in police cells in Nelson for six nights under similar circumstances.
The Hawke's Bay boy's lawyer, Don Kennedy, said the situation was completely unacceptable.
"[Oranga Tamariki] let themselves down quite badly in my view," he said.
"It seems there are just simply not enough beds available given the [Oranga Tamariki Act] says there should be."
The stay had resulted in the boy suffering severe emotional trauma, Mr Kennedy said.
"I saw the mood of my young person change from day-to-day," he said.
"The longer it goes on, the worse it gets... It's what I call heightened anxiety about what's happening."
Oranga Tamariki said it was disappointed both boys had been held for so long, as it was something the ministry had been actively working to prevent.
Deputy chief executive of Youth Justice Services Allan Boreham said it had a duty of care to provide beds for the two boys - and it had failed.
"We don't want to have any young people in police cells if we can avoid it," he said.
"We've set ourselves an ambitious mission not to have any young people in police cells for more than 24 hours in the next three years."
Oranga Tamariki has increased the number of beds available for young people by 25 percent, bringing it to 156, and wanted to increase it even further.
"If a young person is in an adult-like facility it's only detrimental to their health," he said.
"If there's anything that we owe victims of the crimes they might have been involved in, it's that we don't do anything to harden these young people so that they don't become life-long criminals."