The Guardian has been given exclusive access to a unit in West Yorkshire trying new ways to reach the most disturbed children

Visiting Keppel high-dependency unit, home to some of the most traumatised and damaged children in the UK, necessitates the navigation of a labyrinth.

After passing through a series of towering gates crested with razor-wire, a security check precedes a winding journey through the intimidating Wetherby Young Offenders Institution (YOI) in West Yorkshire. A former borstal, built in the 1950s, it is now home to almost 400 young men who, on sensing an outsider, crane through their cell windows to whistle and shout.

After such a buildup, arriving at the modern, small and self-contained Keppel unit on the farthest edge of the children's prison is a surprise.

Close enough to Wetherby racecourse to hear the thundering of hooves on race days, the low-rise block sits on rolling lawns where pet rabbits run free and ducks doze by a well-stocked fishing lake. By the pigeon coops on the far side of a football field, a cockerel crows over a brood of free-range chickens. Around the back of the unit, aviaries house 48 birds of prey.

From outside the unit, built on a former naval base and named after the 18th-century seafaring hero Augustus Keppel, could be mistaken for a holiday camp. Behind the facade lies a very different reality. Keppel is home to 48 boys, aged 15-17, who are capable of such extreme violence – against themselves and others – that the only way mainstream children's prisons could keep them safe was to contain them, locking them in cells, segregation units or secure hospitals.

The menagerie, instead of being a picturesque distraction, is a key part of the therapeutic programme that Keppel is developing. "We often introduce things simply because we have a gut instinct it will be a good idea," says Terry Wilson, manager of the unit. "Often it's pure speculation."

"Instinct" is a rare catalyst for change in the child custody system, where insistence on evidence-based approaches often stifles innovation. Giving the boys a chance to care for animals has been a masterstroke. There has not yet been a single instance of violence towards the creatures.

Before Paul, 16, came to Keppel, the only animals he had seen were rats that gnawed the furniture in the semi-derelict flat he called home. His upbringing revolved around abuse, chaos and trauma. Standing with other children by the lake, he explains why the fishing means to much to him. "When I catch a fish, I feel, you know … " he pauses and shuffles his feet in embarrassment. "I feel proud," he eventually mutters.

Sensing trouble, he slides his eyes towards the other boys. There's a moment when it could go either way. Then another boy blurts out: "I like watching the pigeons raising their chicks together. They're dead loving and caring. I'd not seen that before." His voice trails off. Then another child adds: "The eagles aren't pets: they're wild animals. You have to respect them. Caring for them gives me a sense of freedom."

Keppel is the government's first concerted attempt to get under the skin of these, the most disturbed children in England and Wales. The Guardian is the first newspaper to be allowed behind the scenes of their unconventionalattempt to achieve this.

Despite being stigmatised by the children in mainstream custody – Keppel children tell of how inmates of the YOI spit and shout insults if they get too near the fence – the unit is already being hailed as a leading light in youth justice. And not only by those with an investment in its success.

Dave has three months left of a four-year sentence for sex offences committed when he was 14. A lanky, pale young man, who taps and fidgets his way through the conversation, he considers himself "lucky" to have been sent to Keppel.

"What I did was horrible," he says. "Just thinking about the crimes I have committed is hard but it's only now that I am thinking about them. I've never done that before. That's taken me years and a lot of work.

"If I'd been in a normal YOI, I wouldn't have got this far. In those places, if someone looks at you, they want to kill you. If someone looks at you here, it's because they want to be your friend. It's nice, you know? It's decent. It gives me the space to start thinking about what I've done."

In the outside world YOIs – including Keppel – are controversial. "The Youth Justice Board is trying to put lipstick on a pig by introducing so-called enhanced units into prisons," Frances Crook, the chief executive of the Howard League for Penal Reform, said last week when it was announced that the number of beds in secure children's homes and training centres were to be cut to fund more units like Keppel.

Crook argues that child custody is not an effective rehabilitation strategy. YOIs are, she says, the "cheapest and most basic form of child custody". Their reoffending rate is about 75%.

Frances Done, chair of the YJB, rebuts Crook's accusation of cosmetic solutions. Keppel, she says, represents a genuine transformation in efforts to reform dangerous and damaged children: "It's not realistic to say we should keep all these children out of the prison system but the idea that we should not try to do the best we can for them, because the whole system of young people in custody is not entirely satisfactory, is wrong."

Keppel is certainly different to the mainstream children's prisons of which Crook is so critical. They can hold hundreds of children, with staff to child ratios of around one to 10. Keppel, in contrast, houses 48 children and has a staff ratio of one to 4.5.

Every young person has their own individual plan, reviewed at least once every two weeks. These care plans put a unique emphasis on offending behaviour, victim empathy and on intense engagement with specially trained staff and mental health teams.

It is too early to know whether the unit is working: the first evaluation is due in June. But 17-year-old Ben iknows Keppel is his last chance. "I never thought about my victims before but [after almost a year of intense therapy], now I do," he says. "Now I think about what it must have felt like to have someone do what I did to them."

"I feel really lucky to have come here. I've learned a lot. I never thought I had opportunities before, just committing crime and defending myself."

Due to be released in two weeks, Ben proudly says his local authority has sorted out a flat for him and a college place. "I'm going to walk out of Keppel with a smile on my face," he says, grinning from ear to ear. "I'm going to sort myself out."

Hearing this, Wilson shakes her head quietly. She looks deeply, profoundly sad. Later, in a side room, she explains why.

"Ben will be back here in a week," she predicts. "They haven't got him a flat. There's probably a room in a B&B somewhere but a boy that vulnerable can't fend for himself in a place like that. This is the first time he's trusted adults and felt respected. He's going to feel completely betrayed – and his anger against the world might be all the greater because of that."

She shakes her head and bites her lip. "I hate to say it, but I think he hasn't got a cat in hell's chance of not going straight back to the life he came from."

Wilson is devoted to her work at Keppel. It is, she says, the "best job I have ever had". She has been at the unit since its inception and is responsible for its innovative approach to rehabilitation. But she admits: "I get so much heartache knowing that almost all of these lads will be back. We have had a couple of brilliant successes but they are few and far between.

"We can deprogramme these lads, get them reading, writing, and get their health needs seen to. But if the structure is not there when they go back to their communities, they go back to square one.

"I'm not criticising the youth offending teams or probation," she adds quickly. "It's down to resources. Without resources, what chance do these kids have?"

Sara Snell, governor of the unit, agrees. "The paucity of provision out there for our children can mean they are just being set up to fail." Her voice trails away. "We have had one boy who took his own life after leaving our care."

In some ways, she says, Keppel is a victim of its own success. "We simply need more of these units across the country," says Snell. "We can be dealing with as many as 35 local authorities at any one time. It's hard supporting children who are coming from so far away. Just think of the number of voluntary organisations, housing groups, charities we need to liaise with."

The Ministry of Justice and the YJB know there is a paucity of help when children leave. Four resettlement consortiums are being piloted and there is talk of a "halfway house" to help the boys ease back into the community after release. Legislation going through parliament will force local authorties to foot the bill for custody of children for the first time, a tactic that is showing signs of focusing minds – and budgets – on preventing reoffending.

In the meantime, Wilson grabs at straws: "Though these lads come back time and again, what we do here isn't wasted because surely, there must be a benefit to being somewhere safe, if just for a short time, and to learn that not everybody is bad.

"I cling to the hope that something we do here registers the next time they're about to commit a crime. I can't say that I expect it to stop them committing a crime but perhaps," she says with painful honesty, "perhaps that crime won't be as bad as it might have been. Perhaps the violence they use will be less."