By Winifred Robinson
Inside the Child Prisons
There are currently around 300 children aged 10 to 17 locked up in England and Wales.
Secure units have been in operation for more than 40 years.
Some social workers do not want to lock children up
But where they once housed only the tiny minority of children who commit really serious crimes, more recently they have been used to contain prolific young offenders, the children who can't, or won't comply with community punishments or settle down at home, in foster care or children's homes.
Now the sector is at a turning point and decisions must be made about the future of secure units, who should be housed there and for how long.
After numbers held peaked at 400 in 2003, when there were 28 secure children's homes, there has been a rapid contraction.
Nine homes have gone and five more closures are expected soon. A report for the Department for Children, Schools and Families reported no fall of in need for these places but rather a fall in demand, driven by a change in ideology - some social workers regard locked children up as a failure and a breach of their human rights.
There are concerns, too, about costs.
It is against this background that senior managers invited BBC Radio 4 into the Vinney Green Secure Children's Unit in Bristol, to meet some of the children and to see what staff aim to achieve.
My producer Sue Mitchell and I met a 15-year-old boy, Mitchell, who arrived at the unit from a young offenders' institution where he had tried and very nearly succeeded in taking his own life.
"It was a big place and it just got to me," he explained. "People was hitting me and punching me from the back all the time."
Typically a young offenders' institution will house 400 inmates, a secure unit has around 24; the age group is younger - from 10 to 17 - and the staff-to-child ratio is high (about one to four).
Mitchell was serving a sentence for a street robbery where the victim, another boy, was punched, kicked and stamped on.
He blamed cannabis addiction and a hot temper. "When I start hitting someone," he said, "I don't know when to stop."
At Vinney Green, a psychologist Amy Ostrowski works with children to give them practical strategies for controlling anger, a common problem.
We watched her in action with a 12-year-old boy, who has been sent to the unit by social services for his own protection after being recruited to a drug-dealing gang.
"He's caught up in this gang culture in London," Ms Ostrowski explained. "A lot of the time he commits acts of violence to be accepted by his peers. He hangs around with 15 or 16-year-olds and for him, it is about being accepted by them."
The anger management advises simple ways of keeping calm, including deep breathing or calling to mind a favourite place.
There are two routes into a secure unit, through social services as a welfare placement or through the courts. In practice, there is little real distinction between the criminal and welfare cases - almost all have long criminal records and troubled family histories.
"The majority are in for burglary, robbery, ABH - but you are shocked by their past and what has happened to them," Amy Ostrowski reflects.
"Such a high proportion have experienced physical and sexual abuse and neglect and that is really shocking how parents could do that to their children and also a lot of them have been in care and claim to have been abused."
For some, like Laura, whose abusive relationship with a boy five years older began when she was only 10, the secure unit is a refuge from the constant threat of violence and a chance to get off drugs and drink.
"He kept on beating me up and I tried to get arrested all the time to get away from it. One day he put me in hospital and they thought he had fractured my skull," she said.
"I've been in a secure unit before, I loved it. I felt safe. I was smoking a lot of cannabis and drinking a lot, I was getting really ill from it."
Most children in secure units are aged 14 and the average length of stay is four months. Residents are taught a range of subjects with an emphasis on basic literacy - many have not attended mainstream school for years.
The government report calls for a clearer policy on the use of secure children's units and proper evaluation of what they achieve.
It warns that good work may be being lost if it stops when children leave and cautions that if the closures are allowed to continue, some children will be denied a place in secure care, when that is just what they need.
Two half hour documentaries, Inside the Child Prisons, will be broadcast at 2000 BST on Easter Monday and at the same time the following Monday 20 April.