The Home Office publishes a quarterly snapshot of people detained solely under Immigration Act powers on the last Saturday of each quarter, including a breakdown of children by length of detention. The latest published information pertains to people detained as at 29 September 2007.
Published statistics on immigration and asylum are also available from the Library of the House.
The Border and Immigration Agency is reviewing what statistics are published (all aspects of the statistics, not only statistics on children). A consultation document was issued on 6 December and a copy can be found at
http://www.homeoffice.gov.uk/rds/pdfs07/bia-immig-stat-review-07.pdf