MPs and penal reform campaigners have criticised the change, which comes before the outcome of an inquest next week into the case of Gareth Myatt, 15, who died after being restrained at a secure training centre in Northamptonshire.
Until now staff at the four privately-run secure training centres have been legally allowed to use physical restraint "distraction" techniques - including hitting a child's nose from underneath - only to prevent children from harming themselves or harming others, or to prevent damage to property.
The use of restraint to secure compliance with staff instructions, such as getting a teenage boy to go to bed or clean his room, or as a punishment, has not been permitted in child jails until this change in the rules.
Three weeks ago a coroner called for an urgent review of the use of restraint after a jury returned a suicide verdict on Adam Rickwood, 14, who became the youngest person to die in custody for 50 years after he hanged himself with his shoelaces at Hassockfield secure training centre, Co Durham. He had been forcibly restrained by four staff shortly before his death.
The latest official figures show that restraint techniques were used by staff on 3,036 occasions between November 2005 and October 2006, on 301 children as young as 12 held in the four child jails.
Lord Carlile, president of the Howard League for Penal Reform, said that using this kind of restraint in a widespread manner would only confirm the children in their offending behaviour.
"It is effectively communicating with these children using the language of violence, as if that is the only language they can understand," he said. "We believe this could contravene international law and that the systematic use of restraint involving distraction techniques may amount to torture."
Sally Keeble, a former Labour minister and MP for Northampton North, said she would challenge the change, which had been introduced by a parliamentary back door. "To sneak this change through parliament beggars belief," she said.
The Ministry of Justice and the Youth Justice Board said yesterday that the legal "clarification" of the rules would not lead to more widespread use of restraint.
Their stance has prompted critics to speculate that the change is designed to legalise existing practices.
Graham Robb, chairman of the Youth Justice Board, which is responsible for the centres, said: "This is about maintaining good order and discipline ... Staff within [the centres] deal with some of the most troubled and damaged young people in society. Without order and discipline they will continue to harm themselves and others." He said those who described restraints as "torture" were not engaging in an adult debate. A YJB spokeswoman said to suggest that the centres could manage without these powers did not take into account the reality of dealing with some of the young people involved.