The detention of children of failed asylum seekers should be banned immediately, a refugee group has said.
The Scottish Refugee Council says the coalition government should make good on its commitment to end the practice and not wait for the results of a Home Office review.
Last year, more than 1,000 children were held with their families while awaiting removal from the UK.
Ministers say they try to avoid the practice but cannot rule it out.
It has been reported that families with children facing removal from the UK are being given an ultimatum to leave the country voluntarily or face deportation "within weeks" under a pilot scheme.
The Guardian newspaper reported that leaked documents showed that the programme, launched by the UK Border Agency last month in the north-west of England, is part of the review of alternatives to detaining children.
The UK Border Agency refused to comment on the leaked papers, but a spokesman said: "The new government has been clear in its commitment to end the detention of children for immigration purposes. One of the first actions was to set up a review and this has already changed the UK Border Agency's approach.
"We are focused on finding an alternative to detention that protects the welfare of children, without undermining our immigration laws."
Clare Tudor, the Scottish Refugee Council's policy officer, told the BBC that her organisation wanted "a commitment set in law that would disallow the government at any time in the future to detain children again".
Soon after taking office in May, the coalition government pledged to end the practice of locking up failed asylum families with children.
Last month, Deputy Prime Minister Nick Clegg told the House of Commons it was "a moral outrage" that more than 1,000 youngsters were detained in immigration centres last year.
A Home Office review into one of the most controversial areas of UK immigration policy ended in July, but legislation to put a definitive end to the practice has not still been drafted.
Though there are currently no children in detention, charities that work with asylum seekers say they fear that without specific legal measures there will be no guarantee that they will not be locked up again in the future.
Immigration Minister Damian Green told the BBC: "I am bending over backwards to avoid the detention of children, but we are still not sure that if we said we would never detain a child even for a minute then we would effectively be able to remove families that had no right to be in this country."