Professor Al Aynsley-Green, England's first Children's Commissioner, says the needs of immigrant children are a "very urgent issue", especially those locked up with their parents in removal centres.
A consultant paediatrician, Professor Aynsley-Green spoke at a Refugee Council conference last week. He said: "The way young people are treated by the immigration authorities and the awful facilities where they are being held made the hair stand up on the back of my neck.
"The means of taking families into detention seem to be inadequate and heavy-handed."
Human rights abuses of asylum-seeking children, including young babies, is a key concern for campaign groups. Many are deprived of proper schooling, allowed little exercise and denied access to proper medical care. In one case, a nine-month-old baby spent seven weeks living in detention centres with his parents until the family was eventually released on bail.
Ministers have repeatedly refused to release precise monthly statistics, despite pressure from MPs and children's charities. However, they have now introduced new measures to review cases of children held for more than 21 days.
Yarl's Wood, in Bedfordshire, is now the main place where families are sent when their applications for asylum are turned down. An inspection report on the centre, published earlier this year, revealed that young children were being "damaged" by their experiences of detention. In one case, a five-year-old autistic girl was so badly neglected that she had not eaten properly for four days.
Professor Aynsley-Green's investigation is also expected to look into reports that immigration officers often refuse to believe the age of young immigrants who come to this country alone, even if it is obvious they are children. This means they do not receive the care they need and instead are left to fend for themselves.
Anne Owers, HM Chief Inspector of Prisons, who wrote the Yarl's Wood report, said social workers should be brought in to monitor the cases of children held in detention.