Children of failed asylum seekers will be able to turn to Barnardo's for support while they are being held in new centres for up to a week before being removed from the UK, the Government said.
The children's charity will provide help and support to families in the centres while they prepare for their return, the Home Office said.
Deputy Prime Minister Nick Clegg, who has condemned child detention as a "moral outrage", was accused of "rebranding detention" by some children's groups last year when he outlined the plans. But he has insisted that the new sites, which will only be used as a last resort, will be a "world away from the old immigration detention centres".
Children will normally be kept in the centres for up to 72 hours prior to their departure, but their stays could reach "a week as a maximum", the Home Office said. During that time, it said, Barnardo's will provide key welfare, safeguarding and support services for the families as they prepare for their return.
The Home Office added that families will be free to move around the site, security will be low-key and the centres will not have an institutional feel.
Immigration Minister Damian Green said: "It is crucial that the welfare of children remains an absolute priority during the returns process and the use of this new accommodation will be a last resort. It will however have an entirely different look and feel to an immigration removal centre with a high degree of privacy for each family."
He went on: "I believe our new approach is both fair and humane. We are providing assistance packages and family conferences to ensure families understand their options, and will be trying to ensure that families can remain in the community prior to their departure home."
Under the returns process which began this month, families are given every chance to leave the UK voluntarily before any enforcement action is considered, the Home Office said. Those who have failed in their application to remain in Britain are taken out of the hands of the Home Office and given to an independent panel of experts.
Families are also offered conferences to discuss their return home, and welfare and medical concerns once the appeals process has been exhausted. Assisted voluntary return packages are also offered. Those who refuse the support are be given up to two weeks in which they will be allowed to remain in the community before boarding a flight home.
"Ensured returns", which involve the use of the new pre-departure accommodation, will be only be used as a last resort. But the Children's Legal Centre has said the new centres "appear to be detention by another name".