Children are being "damaged" by their detention at Britain's largest immigration removal centre, the Chief Inspector of Prisons has warned.
Yarl's Wood was built to house up to 405 detainees
Anne Owers said an autistic girl of five had been held at Yarl's Wood and not eaten properly for four days.
She said education at the centre was "inadequate" and "depressing".
The Home Office said detention was used sparingly, especially when children were involved, and education at Yarl's Wood, near Bedford, was improving.
Yarl's Wood was built to house up to 405 detainees, including failed asylum seekers and their families.
In 2003 rioting inmates destroyed half of the building just weeks after it had opened.
Ms Owers said the centre was not equipped to deal with children with special needs.
The autistic girl and her family had been released when her team told managers of her condition.
Three other children had been detained just before sitting their GCSEs, Ms Owers added, but two of them were later released.
"Nobody had looked properly at their situation and circumstances before they went into detention and immediately afterwards," Ms Owers told the BBC.
"Once these processes kick into motion, the children kind of become invisible, nobody looks at what is happening to the child and what damage detention may do to the child.
"There will be other options available to the authorities for keeping a close eye on those people with families."
Ms Owers said children should be detained only in exceptional circumstance and called for "an independent and immediate welfare and needs assessment of each child" affected by a decision on detention.
Detainees were twice as likely to report feeling unsafe at Yarl's Wood as in other detention centres, according to a survey conducted by Ms Owers' team.
Some detainees - particularly African women - also reported poor relationships with staff.
Yarl's Wood is run by a private company, GSL UK Ltd.
Corporate communications director John Bates told BBC News: "Instances when detainees considered centre staff were disrespectful and insensitive to their needs... may have reflected misunderstanding about culturally appropriate modes of expression or behaviour.
"Some detainees objected to male officers being involved in searching women's rooms or looking into them while women officers searched."
Two out of every three detainees asked said staff treated them with respect, Mr Bates added.
Yarl's Wood met "widely praised" Ofsted standards for children throughout the UK, but was "compromised by the difficulties of dealing with a broad range of ability and age" and the fact detainees average length of stay was "two to three weeks".
A Home Office spokesman told BBC News: "Secondary school-age children are now well served by a dedicated teacher in a well lit, lively classroom with an increasing provision of educational resources.
"Whilst we accept that the detention of a child may be unwelcome if a child is preparing to sit examinations, a decision to proceed with removal will be taken only once the family's application for asylum has been refused and their statutory appeal rights are exhausted.
"At this point the family would know that they had no further basis of stay in the UK and would have been expected to leave.
"Detention is used sparingly and for the shortest period necessary and this is especially true for families with children."
Refugee Council spokesman Tim Finch said the chief inspector had sent out a clear message that a detention centre was no place for a child.
"Yarl's Wood is supposed to be the flagship centre for detained children, which is why this report is both disappointing and revealing," he said.