One after another they are brought forward: a 16-year-old charged over assaulting a shopkeeper with a claw-hammer. A 17-year-old on a three-month crime spree, including multiple high-speed chases with police. A 16-year-old who smashed a chair over the head of his cowering mother, then tried to kill himself. The headlines scream of a youth crime crisis and a week spent in the Children's Court paints a confronting picture. But while the intensity of the explosion of young violent offences may be shocking, the scale is surprising also. Many of these crimes, research suggests, are being committed by a tiny group of offenders – perhaps as few as 180. Who are they? According to the Crime Statistics Agency, these youths generally begin offending at around age 10. By the time they are 18 they will have, on average, almost 80 recorded offences. They are in and out of youth detention before graduating to the adult justice system with a long list of priors.

Experts say the system works for most kids, but is failing this group. And they don't know why. "We genuinely don't know what the issues are for these several hundred young people. We need to understand what the drivers of their offending are," says the Commissioner for Children and Young People, Liana Buchanan. Victoria's youth rehabilitation system is among the best in the world, she says. But it is not working for these kids, and nobody knows why. In the days The Age spent in court this week many of the most serious offenders appeared to be from what could loosely be called African backgrounds. But try to explore this notion beyond the anecdotal and you run into difficulty. Experts told The Age there is simply no data available that can accurately show how heavily young African people are represented. The Crime Statistics Agency breaks youth criminals down into four groups. The kid who makes one mistake and learns. The youngster who commits crimes as a young adolescent but comes good as he moves into adulthood. The late developer, whose criminality only blooms as he ages.

And the high offender. These kids start committing crimes at age 10 and never stop. They are disproportionately responsible for the worst, most serious crimes. They are generally extremely disadvantaged, and more likely to be Aboriginal than the other groups, the agency says. There are fewer than 200 of these children in Victoria, the CSA estimates. These ultras are responsible for almost one in four youth crimes. The number of young people being sentenced between 2010 and 2015 almost halved, and Victoria's rate of children under justice supervision is the lowest in the country, per Victorian Sentencing Advisory Council data. But the same data shows this small group of kids, the ultras, are committing more crimes even as the overall youth crime rate falls.

Why? "That's the question that's not being asked," Anoushka Jeronimus, Victoria Legal Aid's youth crime project manager says. "We need to figure out how we respond to these young people. But there is simply no space at the moment to be able to have that discussion calmly and rationally. Because the pressure from the media, it really is extraordinary." One answer: nearly two-thirds of child offenders have been victims of abuse, trauma or neglect, according to Youth Parole Board figures. More than a third have siblings or parents who have been imprisoned. They are victims before they themselves become perpetrators. Many have complex mental health problems, says Ms Jeronimus. "We are dealing with some of the most vulnerable kids you've come across. These are kids, they are threatening self harm from as early as seven. They are children. And they are coming into contact with the system for a reason."

Phillip – not his real name – has been trying to kill himself from a very young age, the court hears. He did not complete primary school. He's 16. High on ice, he got into an argument with his mother over a mobile phone. He grabbed a kitchen chair and broke it over her head. That's not all. He got in a fight with a PSO who capsicum-sprayed him. He beat a middle-aged man and stole his bike. He's already been to jail for a violent assault on a woman. His youth justice case manager takes the stand. Phillip says, she tells the court, that he hopes he will die. Because then all his problems will be over. Nathan is one of those ultras. His rat's tail runs down his shoulders and into the neck of his black hoodie. He's facing 40-odd charges, including aggravated burglary. Again, he was on parole at the time of the alleged offending. Again, he's got pages and pages of priors. His MO is like that of many others that come through here. Steal a car, drive as fast and as dangerously away from police as possible until they are forced to terminate the pursuit – or until someone dies.

Here's another thing you notice when sitting in the Childrens Court: the combination of extreme violence, risk-taking and, well, pettiness. These are not criminals calculating risk and reward. They steal iPads, phones, the things a kid desires. They steal noticeable cars – Mini Coopers, four-wheel-drives, a Jaguar – and drive in convoy, like gangsters, flaunting their stolen wealth. They don't seem to care about being caught, says Ms Jeronimus. In fact, they want the spotlight; this, in part, contributes to the rising number of youth crimes being reported in the media. "What often distinguishes young people and their offending is that it really lacks sophistication. It's far more easy to detect. It's far more high profile because they're not masking their offending." When they steal bankcards, they buy cigarettes. After one teen nicked a car and a bankcard, he drove the stolen Holden through a McDonald's drive-through, using the card to buy $10.25 of greasy fast food.

"You were released on parole, and about halfway through the parole you were involved with drugs, dishonesty and dangerous driving," the magistrate tells Nathan as she denies him bail. His father, his brother, girlfriend and his best friends all attend court. "Love you, brother", they yell as he is taken back to the cells, "love you".