More than 400 children were being held in British immigration detention centres with their families, a report said today, citing official figures.
The Guardian newspaper said 470 children, many from countries suffering poverty and conflict such as Zimbabwe, Sudan, Sri Lanka and Democratic Republic of Congo, were locked up after arriving in Britain.
The figures from the Home Office were provided for a single day, on June 30 this year.
Most of the children were aged under five, and almost one third were held for longer than 28 days, the newspaper said.
Out of 225 children released from detention in the second quarter of this year, only 100 were then removed from Britain.
Critics quoted by the left-of-centre daily said the statistics showed the UK Border Agency was failing in its duty to detain children only "as a measure of last resort and for the shortest appropriate period of time."
The Home Office said: "The UK Border Agency fully recognises its responsibilities towards children but these responsibilities have to be exercised alongside our duty to enforce the laws on immigration and asylum.