The report by HM Inspectorate of Prisons found widespread variation across secure units and that black and minority ethnic (BAME) young people are more likely to be victimised by staff.
It found that 32 per cent of children in Medway Secure Training Centre (STC) said they had been victimised by staff while more than half (53 per cent) of children at Feltham Young Offender Institute (YOI) reported such incidents.
Across the youth secure estate 42 per cent of children and young people had been victimised by staff, says the report which looked at 12- to 18-year-olds' experience of custody during 2018/19.
The most common form of victimisation by staff was verbally abusing children, cited by a third of victims.
Meanwhile, two per cent of victims said staff had sexually assaulted them. Those from traveller communities are more likely to report such incidents with 13 per cent doing so compared with one per cent of their peers.
Around a fifth of all children (21 per cent) say staff threatened or intimidated them. More than one in 10 (12 per cent) say they were physically assaulted and a similar proportion (10 per cent) say staff stole their property.
BAME young people are more likely to be abused and feel it is unlikely that any complaints they make about victimisation will be dealt with.
The report found that 38 per cent of BAME children had been verbally abused, compared with 28 per cent of white children.
A quarter (25 per cent) of BAME children said staff had threatened or intimidated them, while the figure is 16 per cent among white children.
When the young people made a complaint only 28 per cent of those from BAME backgrounds said this had been dealt with fairly, compared with almost half (47 per cent) of their white peers.
Among all children, 14 per cent said they were “too scared” to make a complaint.
The inspectorate is concerned about the use of physical restraint by staff on young people, particularly at England’s three secure training centres Medway, Rainsbrook and Oakhill.
“Most children placed in these establishments had experienced use of force and had been physically restrained,” says the report.
“Furthermore, there remained a significant amount of work to be done in all three centres to ensure fairness and consistency was applied in behaviour management, as well as ensuring that children’s positive behaviour was well promoted.”
Almost two thirds (64 per cent) of children placed in STCs said they had been physically restrained. Of these around a third of children (31 per cent) were not spoken to about the restraint by a member of staff afterwards.
Children in the secure estate are also spending long periods of time alone.
Seven out of 10 (71 per cent) children are allowed out of their cell for more than two hours on weekdays but during weekends only a quarter (27 per cent) of inmates are out of their cells for more than this length of time.
Around three in five children (59 per cent) said they had been separated from their peers as a punishment, by being locked up or stopped from mixing with other children.
Justice charity Nacro’s chief executive Campbell Robb said that children in custody are facing “wholly unacceptable conditions”.
“Not only are these conditions inhumane, they are ineffective and often make things worse,” he said.
“With nearly seven out of 10 young people released from prison reoffending, we desperately need to change. The government must commit to a fundamentally different approach to working with children swept up into the youth justice system.
“The system has for too long been under-resourced and overlooked. It’s time to treat children as children and give those who have made mistakes the best chance at a second chance.”