Too many children are being held for long periods at a UK immigration centre, according to figures obtained by the BBC.
The government said detention was sometimes necessary
Many of those held were not deported and the chief inspector of prisons has said children should only be detained there "in exceptional circumstances".
The government admits detention was "not ideal" but sometimes necessary.
Immigration minister Liam Byrne said he personally checked the case of every child held longer than 28 days.
The BBC request to the Home Office found that between October 2005 and September 2006, 1,160 children (aged under 18) were held at Yarl's Wood.
Of those, 675 were removed from the UK, while 445 were granted temporary admission or released. A further 40 were bailed.
The figures also show that 115 children were held for more than 29 days and 70 of them were later either granted admission, released or given bail.
Ugandan mother-of-two Trudi, from East London, is trying to claim political asylum and has been detained twice with her two children at Yarl's Wood.
"The children found it very upsetting. They kept on asking me if we are in a prison and whether we had committed any crime.
"They still have nightmares, they don't sleep, they think about detention."
Chief Inspector of Prisons, Ms Owers said: "There should be consideration of the welfare of the child.
"We know it can't be paramount but it should be considered so you need to show that detention is necessary, given that it's inevitably going to effect the welfare of the child.'
Liam Byrne, Minister for Immigration, said: "There are teams of social workers and healthcare professionals who make sure there are very regular reviews of children and their families as well both at seven days, 10 days, 14 days.
"I look at all cases personally once a child has been detained after 28 days in order to authorise it myself.
"It's not an ideal environment in which to keep children and that's why its often so frustrating that parents drag out the deportation process."