The National Offender Management Service (Noms), which oversees the secure estate for the Ministry of Justice, has recommended to YOIs that for every 12 young people there should be one officer as the minimum staffing standard.
Currently, child-to-staff ratios differ across YOIs, however some have ratios of 10 young people to one prison officer.
The move could see staff numbers at YOIs reduced, raising concerns among youth justice campaigners about inmate welfare and the ability to deliver effective interventions.
The introduction of the new ratio is part of a Noms review of staffing at YOIs across the country in light of a big fall in the number of under-18s in custody in recent years.
Despite the recent fall, YOIs have struggled to recruit and retain staff. A senior source added: “YOIs haven’t got enough staff and there are a lot of concerns in the youth estate about this."
A Prison Service spokesperson said: "The new ratio for the under-18 YOI estate is part of a wider programme of work to standardise services and resources which, up until now, have varied significantly.
"The changes, which will in places actually increase staffing levels, will only apply to officers working on the main residential units and will not compromise the security and safety of prisons.
"We are committed to reducing costs for the taxpayers and where this means reducing staff numbers, we will work constructively with trade unions to avoid compulsory redundancies as far as possible."
The number of under-18s held in the secure estate is currently at its lowest level in more than a decade, having more than halved in the last four years to the current level of 1,320.
Penelope Gibbs, chair of the Standing Committee for Youth Justice, said: “Children in YOIs need a lot of intensive support and it is a lost opportunity if staff are cut.
“Given that the numbers in child custody are going down, money should be saved by closing institutions, not cutting staff.”
Andrew Neilson, director of campaigns at the Howard League for Penal Reform, said: “Having a high number of staff to children is an important part of running a good prison, where relationships are healthy and problems such as violence are kept to a minimum.
“Given we know that children’s prisons tend to be the most violent jails in the country, it would seem perverse to reduce the number of staff on duty.
“It is welcome that the children’s prison population has fallen and that prisons are not running at full capacity.
"But that is an argument to close prisons and reorganise the secure estate rather than diluting the care that these children receive.”
A consultation on the future of the youth secure estate closed last month.
