Convicted 12-year-olds could be imprisoned from this autumn - despite being likely to benefit least from this form of punishment - because of the timetable under which new laws are being enacted.
Paul Cavadino, principal officer for the National Association for the Care and Resettlement of Offenders, said the problem stems from Government legislation that lowers the age of imprisonment. This will come into force this autumn, before other support schemes are in place.
"Custody comes first, non-custodial options second, which is giving us cause for concern," he said.
He told NACRO's Youth 2000 conference in Sheffield that the Crime and Disorder Bill - expected to become law this summer - would depend crucially on "youth offending teams" being set up by local authorities. The scheme is to be piloted from this autumn and become statutory in April 2000.
The teams will consist of representatives from police, probation, health, education and social services, and will be required by law to formulate and implement a yearly youth justice plan.
Mr Cavadino urged delegates to start planning now to establish their teams, as the powers to lock up children would be given "alarmingly soon".
Services must work together to ensure that bail support schemes and supervision programmes have the maximum impact in diverting young people away from crime and custody, he said.
Mr Cavadino added that the Crime and Disorder Bill potentially provided a framework for a more consistent and effective approach to youth crime. Responsibility had shifted from the courts to the community, the elements of which must work together.
Helen Edwards, NACRO's chief executive, said that tackling youth crime must be placed before vested interests. She said the various agencies had to work together more effectively.
Lynda Hoare of the Social Services Inspectorate welcomed signs of greater co-operation between agencies. She cited the invitation from Sir David Ramsbottom, the chief inspector of prisons, for her to take part in his recent inspection of young offender institutions.
But she said everyone concerned with young people would have to adjust very quickly to different ways of working.
Alun Michael, Home Office minister, told the conference that he had found a positive response to the Bill, saying: "There's a will for change to carry it through."
But reforms to the youth justice system were not enough to solve the problems of youth crime, he said. Other Labour initiatives such as expanding nursery education, raising standards, the welfare to work programme and the New Deal would also play their part.