Unaccompanied child asylum seekers who are denied the right to stay in the UK are to be deported before they reach 18, the government has announced.
The government wants to handle child asylum claims more quickly
Currently, the Border and Immigration Agency waits until the young person turns 18 before beginning proceedings.
Children's rights campaigners say the move could put those being sent back at risk on their return.
The government said authorities would not deport children until they were "100% sure" of a safe reception.
About 2,000 unaccompanied children seek asylum in the UK every year.
Immigration minister Liam Byrne said the current policy was a "green light" to organised gangs of child traffickers who knew children would not be sent home once they were in the country.
But Donna Covey, chief executive of the Refugee Council, said: "The government should not try to force any child to return against their wishes where their safety and welfare cannot be guaranteed.
"These are not children who come here seeking a better life, with their families waiting for them in peaceful homes. Many of them are children from war zones."
Sir Al Aynsley-Green, Children's Commissioner for England, said he welcomed the government's efforts to tackle the problem, but he remained concerned about plans to withdraw support from unaccompanied children, especially those from "conflict-affected countries".
"If they feel unsupported in the UK, these children could disappear from a local authority's care well before their 18th birthday. This puts them at serious risk of harm..."
Children's charity the NSPCC said children who were frightened, alone and may not speak English would now be forced through an asylum process which was unsuitable for children.
It has called for the government to give separated children a right to an independent guardian to help them understand the process.
The policy change comes as Mr Byrne announced a series of measures aimed at handling child asylum claims "swiftly and compassionately".
better procedures for identifying and supporting unaccompanied asylum seeking children who are the victims of trafficking
locating unaccompanied asylum seeking children with specialist local authorities to ensure they receive the services they need
speedier decisions on immigration status to ensure integration into the UK or fast return to a safe country of origin.
The government will also introduce new procedures to assess the ages of asylum seekers to help stop adults posing as children.
One suggestion, which will be consulted on further, was to force asylum seekers to undergo dental X-ray checks to assess their age.
Critics though said it was a step towards treating youngsters as suspect immigrants, not children.
The Home Office also announced it was consulting on a new code of practice on how immigration officers deal with children and on whether the UK should extend its commitment to the UN convention on rights of the child to include immigration cases.
This would follow the lead of most other European countries.