A spate of violent offences carried out by young people recently is extremely concerning, police say.
This week a 62-year-old woman suffered a serious head injury during a carjacking.
The police have arrested and charged a 14-year-old boy with the attack.
Earlier this month a 17-year-old girl was charged with aggravated robbery, theft and unlawfully taking a motor vehicle following another carjacking.
Nancy Voon, 65, had just pulled into the Panmure YMCA carpark when two people, including the 17-year-old, dragged her from the car and attacked her.
Two other teenagers, both under 17 and in CYFs custody, were spoken to by police.
And five 16-year-old boys were charged with armed robbery after robbing a North Shore electronics store.
Police said the boys brandished an axe and metal bars during the robbery and chased and kicked one of the workers in the face.
Police National Youth Manager Inspector Ross Lienert said there had not been a statical increase in youth crime - but the police had noticed an increase at the serious end of offending.
"Trends over the last five years have seen an increase in the nature of offending," he said.
"29 percent of young people between the age of 14 and 16 are committing medium to high-level offences."
In 2010, 25 percent of the same age group were committing serious offences.
"It's important that we acknowledge youth offending has dropped something like 50 percent in the last five years - but the sector has been struggling with the more serious end of crimes - it is concerning," Mr Lienert said.
"There are a lot of factors to play; these young offenders generally come from shocking backgrounds where they've been brought up with family violence, drugs and alcohol - and I guess we see the end result of that when we get this serious offending."
The intention for police was to stop re-offending, he said.
"With the serious offenders we have struggled to do that and we are open about that - but there is a lot of work going on behind the scenes.
"There is the Youth Crime Action Plan and the Ministry for Vulnerable Children will play a large role in helping with youth offending."