Child migrants from the Calais "Jungle" camp will not face dental checks in the UK to verify their age, the government has insisted.
The BBC understands 39 children have arrived this week, but there have been questions whether some may be adults.
Conservative MP David Davies called for mandatory teeth checks to reassure the public, but the British Dental Association said this was unethical.
The Home Office said the migrants would face different checks once in the UK.
"We do not use dental X-rays to confirm the ages of those seeking asylum in the UK. The British Dental Association has described them as inaccurate, inappropriate and unethical," the Home Office said.
It is understood that further checks to be carried out will include interviews with relatives in the UK and fingerprinting to cross-check with other records which may contain age details.
One 14-year-old migrant, who arrived from Calais on Monday to be reunited with his older brother, said he had to get documents to prove his brother was in the UK, and was interviewed twice in Calais by French authorities and the British.
He was interviewed again once in the UK.
In Calais, the young Afghan boy looked strained, rubbing his hands together nervously on a chilly morning. But, after a 100-mile journey, and on the other side of the Channel, his face broke out into a broad grin.
His dream of a new life was within reach.
The setting was a back entrance to a drab government building in Croydon, but as officials ushered him towards the next step in the asylum process, well-wishers greeted the 13-year-old with whoops and cries of "well done".
His long journey, which he shared with singer Lily Allen in a BBC Victoria Derbyshire film last week, began when he fled his home country to escape the Taliban.
His father sold his land to pay to send his young son to Europe.
But the slow legal process in Calais kept him there for two months, and every night he made a fresh attempt to stow away on lorries to reach the UK.
Now, he can look forward to being reunited with his family and starting school in England.
The new arrivals were placed on a list drawn up by the charity Citizens UK, which is working with the government to bring unaccompanied minors over from Calais.
The list was ratified by French authorities, who would have carried out interviews with the children before they could travel to the UK. If they have no proof of age, officials consider their looks and demeanour.
But since the migrants' arrival in the UK, photographs of some have appeared in newspapers alongside headlines questioning their age.
Mr Davies, Monmouth MP, said that one of the migrants arriving had "lines around his eyes and looks older than I am".
He said: "If they are jumping on lorries, they are not going to be adverse to lying about their ages. We should do the tests."
Fellow Tory MP Jacob Rees-Mogg, who is also calling for more stringent checks, said it was "very worrying" that "older migrants are reported to be pushing children out of the way".
But the British Dental Association, which represents UK dentists and dental students, said it was unethical to expose individuals to radiation and was an inaccurate way to check ages.
Diane Abbott, Labour's shadow home secretary, called dental checks "an outrageous demand, which would further violate the human rights of vulnerable refugees".
And the Equality and Human Rights Commission said the tone of the discussion was becoming "irrational", adding that the "best way to protect children's rights is to treat them as children until proven otherwise".
One of the pictured "child migrants" is described by the Sun newspaper as looking 40 with crow's feet around his eyes.
But Citizens UK said it was thought this was a translator who was accompanying the children.
British Red Cross charity worker Vanessa Cowan, who travelled with 14 of the migrant children, said they were "small boys" who seemed "quite young".
"The perspective of the pictures or just the way the picture is taken could be deceiving and the boys that we brought were small boys," she said.
The Home Office received 3,472 asylum claims from unaccompanied individuals claiming to be children in the year to June 2016.
Of those, 933 claimants had checks carried out on their age, and 636 were found to be adult, the Home Office said.
If any of the latest arrivals are found to be over 18, Home Office sources say it would be extremely unlikely that they would be returned to Calais as they would be entitled to claim asylum in the UK regardless of their age.
French authorities have said they will close the Jungle camp - near the port of Calais and close to the 31-mile Channel Tunnel - by the end of the year.
UK officials in Calais have been focusing initially on unaccompanied minors who have the right to join relatives in the UK under EU legislation, known as the Dublin regulation.
Under the EU-wide regulation, asylum claims must be made in the first safe country a person reaches, but children can have their claim transferred to another country if they have relatives living there.
Update 21 October 2016: It was subsequently confirmed by the Home Office that the person thought to be a translator was in fact a migrant.