Hundreds of children in custody were already among the "most vulnerable individuals in our society" before they were slapped with a prison sentence, doctors have warned.
The British Medical Association (BMA) said numerous services were letting down the most vulnerable children in the UK by putting them behind bars when alternatives to custody should be considered.
The BMA also called for an end to holding children and young people aged 17 and under overnight in police cells.
A new BMA report, "Young Lives Behind Bars: The health and human rights of children and young people detained in the criminal justice system", said many children in detention reflect a failure by society to protect them.
Dr John Chisholm, chair of the BMA's Medical Ethics Committee, said:
There were 1,544 youngsters in custody in England and Wales in 2012/13.
According to the BMA:
- Three quarters of children in jail have lived with someone other than a parent and 40% had been homeless in the six months before entering custody.
- Some 24% of boys and 49% of girls, aged between 15 and 18 and in custody, have been in care.
- Around 60% of children in detention have "significant" speech, language and learning difficulties, while 25 to 30% are learning disabled and up to 50% have learning difficulties.
- More than a third of children in custody were diagnosed with a mental health disorder, the report added.
Juliet Lyon, from the Prison Reform Trust, told Good Morning Britain youngsters who ended up in psychiatric care had a shot at finding out "what went wrong in their lives," as they had access to care.
However, vulnerable youngsters who were given a custodial sentence did not have access to expert help and would often go on to reoffend.