Children are no longer to be detained in detention centres like Yarl's Wood in Bedfordshire or Oakington in Cambridgeshire.
The new government announced the end of the practice in the Queen's speech on Tuesday.
Yarl's Wood has been the main removal centre holding women and families facing deportation for many years.
Chief prisons inspector Dame Anne Owers said in March some children were being held at Yarl's Wood unnecessarily.
And her report said half the centre's children were later released because they were either no longer facing removal or were being allowed to live normally while legal appeals were considered by the courts.
Each year, about 2,000 children were held at the centre for an average of 15 days.
There have been a number of protests at Yarl's Wood, including a hunger strike by women reported to be campaigning against their length of stay at the detention centre.