Unaccompanied teenagers claiming asylum could be forced to have dental X-rays to prove their age, immigration minister Liam Byrne has told MPs.
Removals: Ministers have pledged to increase rates
Children's charities have criticised the practice which was banned in 1982.
But Mr Byrne said it could not be ruled out as part of a clampdown on adult asylum seekers posing as children, to be announced next week.
He also said it would take five years to clear the backlog of asylum seekers, prompting criticism from the Tories.
Echoing comments made last year by Home Secretary John Reid, Mr Byrne said the Immigration and Nationality Directorate was still several years away from being able to consider 90% of asylum claims within six months.
"It is going to take us until about three or four years time before we are able to consider 90% within six months," he told the joint committee on Human Rights.
"There is still going to be a time ahead of us before we get these processes as straight as they should be. It is going to take us four or five years to work through the backlog ahead of us."
Shadow home secretary David Davis said Mr Byrne's "admission" showed the utter chaos in the asylum system".
He added: "On current net removal rates it would actually take the government over a century to clear the backlog of outstanding cases and remove all failed asylum seekers who are here but should not be."
The committee was told there has been a big increase in the number of adult asylum seekers trying to pass themselves off as children.
Jeremy Oppenheim, director of the National Asylum Support Service, said there were "considerable incentives at the moment for them to claim to be younger than they are".
But new proposals, to be announced next Tuesday, "will attempt to address that", he said.
He said dental X-rays - banned for the age determination of children by former Conservative home secretary William Whitelaw - have been piloted by some local authorities as a potentially more accurate way of establishing the age of claimants than visual checks.
Unaccompanied asylum seeking children
3,445 under-17s assessed in 2003:
4% granted asylum
32% granted exceptional leave to remain
40% granted humanitarian protection
Source: Home Office
Children's charities have criticised the practice as traumatic for vulnerable children claiming asylum and even dangerous for their health.
But immigration minister Liam Byrne told the committee their greater use could not be ruled out.
"What we can not get away from is that we must have in place the most effective systems for determining a child's age," said Mr Byrne.
"Now if it is true that a dental X-ray is able to establish with a more precise range an individual's age than, for example, any other form of X-ray, or any other form of determination, then I think we have got to really look very hard at that evidence.
"Because we cannot have adults in the children's system. To have adults in the children's system I believe poses a serious threat to our obligation to protect children effectively."
Mr Byrne said he did not want to give full details of the proposals, which will be announced in the Commons.
But he said they would also include plans to relieve the burden on social services in London and the South-East, where most unaccompanied asylum seekers arrived in the UK.
At the moment, councils near ports and airports are obliged to look after child asylum seekers until they reach adulthood leaving at least one local authority, near Heathrow, on the brink of financial crisis.
Mr Byrne said: "I think there is a strong argument for centres of excellence around the country, which would allow us to move numbers, potentially, out of the south-east where there are particular pressures on children's services."
The current policy, "which leads to a sharp concentration of unaccompanied asylum seeker children in the South-East is not sensible," he added.
But he said he could not guarantee there would be any extra money for local councils to deal with unaccompanied asylum seeker children.
Mr Byrne also said he was "exploring alternatives" to locking up children facing deportation - but until he could stop their families absconding he could not end it.
A pilot scheme in Scotland aimed at ending "dawn raids" on families facing removal had "failed dramatically" said Mr Byrne.
Only one out of the 141 families asked to volunteer themselves for removal had turned up to be deported.
"Voluntary checks have not just failed but failed very dramatically. Detention is part of the toolkit that is available," said Mr Byrne.
But he said it was "very expensive" and it had to be used in a more intelligent way.
He also stressed that families should not be held in detention centres unless they had a "clear" date for deportation.
Commenting on the dental X-ray plan, shadow immigration minister Damian Green said: "Any practical and well-targeted measure that will reduce fraud in the asylum system would be supported by us as it should be by all responsible people."