Seeking Sanctuary, which has worked extensively with children in the 'Jungle' migrant camp, said the proposal from Conservative MP David Davies was "un-Christian" and that a believer should respond to these children with "humanity".
David Davies, the MP for Monmouth, suggested that dentists should check the teeth of migrants coming live in Britain to make sure they weren't lying about their age.
It's after the first unaccompanied children were brought into the UK earlier this week (below). Some newspapers have questioned whether they were under the age of 18 - a specific parameter for their asylum.
Home Office figures have revealed more than two-thirds of refugees (68 per cent) who've had their ages assessed in the last year were found to be adults despite claiming to be children.
In the last ten years, 45 per cent were found to be over 18.
Ben Bano, from Seeking Sanctuary, told Premier's News Hour: "We think this is unethical, unnecessary and un-Christian.
"The British Dental Association have been quite clear that these checks are very unreliable, so our view is that this is not appropriate.
"A Christian response should be one of humanity and compassion. These children, and particularly those who're being prioritised, are those who're in danger of being trafficked.
"Let's get them to safety first and then we can deal with the issues afterwards."
Fr Michael Scanlon from St Mary's Church in Croydon, south London, has been providing support for Calais asylum seekers waiting to see their loved ones.
He told Sky some of them didn't look young: "There have been a few, two or three, that have looked older than 16 or 17.
"But the world they've lived has been very tough and very hard going."
Listen to Premier's Hannah Tooley speaking to Ben Bano on the News Hour: