International trafficking networks have used a children's home near London's Heathrow airport as a "clearing house" for dozens of youngsters smuggled into Britain, it is reported.
A leaked document from the UK Border Agency showed that since March 2006 at least 77 Chinese children have gone missing from the facility.
Run by the London borough of Hillingdon, it is believed the children have been forced to work in prostitution or the drugs trade.
The report, obtained by The Guardian and marked "restricted", revealed how unaccompanied Chinese children arriving at Heathrow are picked up by border officials and taken into local authority care, only to vanish within days or weeks.
It said 10 children had jumped out of windows, some had disappeared during fire drills and others simply walked out of the building into waiting cars.
Only four were found. Two girls, one of them pregnant, later reappeared after being forced to work in brothels in the Midlands.
It is believed many are coerced into prostitution, working on cannabis farms or selling counterfeit goods on the streets.
The document said the missing children were victims of an international trafficking network with agents based in countries including China, Brazil, Japan, Malaysia and Kenya.
Shadow home secretary Chris Grayling said: "To have such a large number of children going missing when they are supposed to be in care is unacceptable. We need an urgent explanation from the Home Secretary."
Hillingdon council said the disappearances appeared to be "planned and co-ordinated by criminal gangs".