Green Party social development spokeswoman Jan Logie said the plan was heartless and illogical, whether it was called a boot camp or a "wraparound service".
"Similar programmes trialled in New Zealand have actually led to increased reoffending by young people."
Logie said the plan to fine parents of young people on the streets between midnight and 5am was ridiculous, given family and sexual violence drives many children onto the streets.
And New Zealand First social development and youth affairs spokesman Darroch Ball said the policy was a U-turn, after National for nine years insisted there wasn't a problem with youth justice.
"Clearly this is merely a reactive policy from National and they're just chasing votes from dairy owners five weeks out from an election, after years of inaction and denials."
New Zealand First wants to introduce a demerit points system for youth offenders, and give young offenders Army-run trade training.
Justice Minister Amy Adams announced National's new policy yesterday, under which judges will be able to send the most serious youth offenders to boot camp at Waiouru for up to a year, and police will be able to issue instant $200 fines to parents of children wandering the streets from midnight to 5am.
She said she would allow the Youth Court to compel parenting education courses on parents even if they discharge the charge against a young person.
She said if National was returned to Government, it would introduce a new classification of offender, young serious offender, targeted at a group of about 150 hardened young criminals aged over 18 who committed a large number of offences.
Instead of being sent to prison, they would be sent to the New Zealand Defence Force-led Junior Training Academy at Waiouru. They would get support there to address problems like addiction or a lack of literacy and numeracy skills, helping them lead better lives while keeping the public safe, she said.
"Those who fail to complete their time at the Academy will serve a commensurate adult sentence of imprisonment instead."
An estimated 50 offenders would be sent to the academy each year in a scheme that would cost $30 million over four years.
In response, Labour justice spokesman Andrew Little said boot camps did not work. They turned young criminals into fit young criminals.
Act leader David Seymour said National had previously announced a boot camp policy - John Key in 2008 in Opposition - and the party had failed because National did not want to commit to addressing youth crime beyond slogans.
In June, Police Minister Paula Bennett said a spate of dairy robberies were being carried out by a hard core of young offenders. Teenagers who would have once rebelled by tagging or fighting are now committing aggravated robberies as part of a new "sub-culture", she said.
Earlier this year the Government announced $1.8m would be made available for robbery prevention at dairies, superettes and small local businesses.
