Most families are held at the Yarl's Wood detention centre
Children held in UK detention centres are not getting the medical care they need, a leading medical journal warns.
An editorial in the Lancet says the 2,000 children held each year miss out on vaccinations and highlights concerns raised about individual cases.
It says a new Immigration and Citizenship Bill proposed for next year should rule out routine detention of children in the future.
The Home Office said all children receive the care they need.
Many of the children are from families who have been refused asylum or have overstayed their visas, while some are asylum seekers or are detained on arrival because they have no identification papers.
Families can be taken from their homes with no time to pack even essential medicines and clothes.
Most go to Yarl's Wood Immigration Removal Centre in Bedfordshire.
The Lancet says children there are "essentially imprisoned with little to do, and provided with inadequate education and health care".
They can often miss out on routine jabs which would protect them against diseases such as measles or meningitis - but then be returned to countries where those diseases are prevalent and are a common cause of death.
Nick Lessof of the Royal College of Paediatrics and Child Health advocacy committee told The Lancet that he saw two children with sickle-cell disease, who had both had a high fever, in Yarl's Wood in May this year.
The children's courses of penicillin had been stopped and they were unable to take fluids, yet they had not been admitted to hospital.
Earlier this year, Frank Arnold of Medical Justice examined another child with sickle-cell crisis who had not been given adequate painkilling treatment and was expected to walk, despite being in pain, from his room to the health-care facility to obtain the treatment.
The Lancet adds: "These appalling failures in the health care of children in detention centres are the ultimate responsibility of the UK Home Office.
"They are in marked contrast to the UK government's global health strategy, Health is Global, which emphasises the government's responsibility 'to improve the health of people across the world, and in particular people in the UK'.
"It is noteworthy that the government is committed to halting and reversing the spread of HIV/Aids, to reducing the incidence of malaria, and other major infectious diseases, and to doing all it can to increase child survival - except it seems in its own detention centres."
The magazine says the planned Immigration and Citizenship Bill, scheduled for parliamentary debate in early 2009, currently available for consultation is "an opportunity for more radical change."
It calls for an end to the routine administrative detention of children.
"If the courts accept that detention is necessary, those few children should receive the same standards of primary and specialist health care as other children in the UK."
A spokeswoman for the Home Office's UK Border Agency rejected the criticisms.
She told the BBC that although she was unable to comment on individual cases: "If a child is in our care and requires medical treatment of any kind we will ensure the child will receive that care.
"Our centres have been praised by independent monitors and our medical care is as good as on the NHS. There is 24-hour nursing care, doctors on call night and day, and access to social workers and dentists.
The spokeswoman added: "Nobody wants to detain children, and it only ever happens as a last resort. When it does it's so we can keep families together, and because their parents refuse to go home despite having no right to be here.
"Our removal centres provide care with the utmost sensitivity and compassion in really difficult circumstances."