Half of social worker posts in young offender institutions (YOI) are lying empty, putting young people at increased risk, a charity has suggested.
According to figures from Barnardo's, there were 10.5 social worker vacancies recorded against 21.5 designated posts in March 2010.
There are 15 young offender institutions across England and Wales housing 15 to 17-year-old males and 17-year-old females who have been given a custodial sentence.
Social worker posts in young offender institutions were introduced in 2005. The Youth Justice Board (YJB) initially provided funding for three years, after which responsibility for providing the posts was handed to local authorities.
The charity, however, claimed there continued to be a lack of clarity over funding, contributing to the shortfall.
Barnardo's chief executive and former director general of the Prison Service Martin Narey said: "No matter what children have done before being locked up, they need to be held in safe custody.
"Most children in YOIs have committed non-violent crimes and are not a danger to others. But they are, so very often, a danger to themselves. There are four instances of self-harm every day in YOIs.
"I find it astonishing that at a time when the necessity of 'safeguarding' children has permeated every part of the public services we should be allowing these posts to disappear."
The Local Government Association (LGA), which represents councils, said attracting applicants was a significant barrier to filling vacant posts.
An LGA spokesman said: "Being a child social worker is one of the toughest jobs in Britain, and for councils it is the toughest job to fill. Making social work a career which more people choose and more people remain in depends on solving a vicious circle of staff shortages and low morale."
