The Howard League For Penal Reform is to condemn the treatment of children in young offenders institutions.
Local authority units are an alternative to custody
Pain and injury are used to control child inmates, it will tell the United Nations Committee on the Rights of the Child later.
A report by the Howard League also claimed that segregation blocks were like modern-day dungeons.
The group's director Frances Crook warned that sending children to custody could be damaging to them.
The report has also highlighted several cases of child deaths in custody and attacked the lack of exercise in young offenders institutions.
Ms Crook said: "We are sending far more children into penal custody, which in itself is a very damaging experience and can condemn them for the rest of their lives.
"Children hardly ever get any outside exercise. Ninety per cent of them, almost, go on to commit another crime."
She added: "If a child, in extreme circumstances, does have to go into custody that should be in the local authority units, many of which are very good and have a very good success rate and so far no child has died in one of the them."