MPs have urged ministers to continue with plans for new so-called 'secure schools' to tackle high levels of violence and self-harm in young offenders' institutions.
A report by the Commons Justice Select Committee has raised a number of issues with existing youth detention settings including some under-18s being effectively held in solitary confinement and an increase in the use of force by staff.
However it noted that 70% fewer children were being detained than in 2010, with a "few hundred" under-18s now held in custody.
The first secure school was due to open in Medway, Kent late last year, to replace the Medway Secure Training Centre which closed in March 2019, but it is now not expected to be operational until 2022.
Secure schools aim to provide educational rehabilitation for children aged 12-17 who are remanded or sentenced to youth detention accommodation.
The committee's Conservative chairman Sir Robert Neill said: "We're pleased about the big reduction in the number of children and young people in detention.
"But those that remain are a big challenge; we salute staff who are doing their best to help them. We agree with the Minister of Justice, Lucy Frazer, when she says the concept of 'secure schools' is a good way to tackle these children's needs. This is better than trying to bring education into inappropriate youth prison settings."
He added: "We strongly recommend - and call on the Ministry of Justice to guarantee - that the first secure school will open in 2022."
MPs have also called for an explanation from the Ministry of Justice and Youth Custody Service as to why the "sanctioned use of force has been rising" within existing young offenders' institutions, secure training centres and secure children's homes.
And the cross-party group said self-harm "reached its highest level in five years" during its inquiry but there was evidence it decreased during the COVID-19 pandemic.
The committee said it was "concerned that the youth estate in its current form is not meeting the needs of the children being held".
In the year ending March 2020, there was an average of just over 780 children in custody at any one time, down from around 2,400 a decade earlier.
The Ministry of Justice said the first secure school would be open "at the end of next year".
A spokesman said: "Secure schools are a revolutionary approach to youth custody and no successful revolution happens overnight.
"Self-harm and assaults have fallen by 17% and 39% respectively in the last 12 months in young offender institutions and we're investing around £5 million to give youth custody officers degree-level training so that they can support these vulnerable children even better."