Fourteen teenagers have arrived in the UK from Calais as a fast-track system was launched to transfer youngsters from the "Jungle" camp before it is demolished.
The Home Office confirmed a group of vulnerable children, aged 14 to 17, were transferred to Britain on Monday morning.
Despite many being told they would have to wait another day to see their loved ones, there was a brief reunion between one man and his nephew whom he had not seen for seven years - through the window of a minibus.
As the group were loaded on to the vehicle after a day of assessment and screening at the Home Office building in Croydon, they had a chance to embrace through the open window.
The man, Jan Ghazi, 37, from Wallington, south London, said seeing his 16-year-old nephew Haris was like a "dream".
He said: "Seven years. It was when I saw his eyes, from when he was a child seven years ago - I recognised his eyes. This was not enough after seven years, it was like a dream."
Haris had made a harrowing journey to the squalid camp in Calais from Afghanistan, his uncle said, fleeing with his brother, who was later killed by people smugglers in Iran.
Another tearful reunion came when two brothers were reunited for the first time in more than a decade.
Asif Khan, a 25-year-old chef who has been living in the UK for 11 years having fled Afghanistan, was allowed to go home with his brother, Aemal, 14, who had been stranded in the Jungle for six months.
He said: "It was a lovely moment, it was so lovely. To get to see him after 11 years, it is just a beautiful day, it was the first time in 11 years I have been so happy. I gave him a hug and cried."
A spokesman for the Home Office said: "This is the start of the process to transfer as many eligible children as possible before the start of the clearance, as the Home Secretary set out in Parliament."
The remainder of the young people who did not leave with relatives are to be cared for in specialist temporary accommodation for a short period before they are reunited with their loved ones, the Home Office said.
The arrival of the group, made up of youngsters who are said to originate from a variety of war-ravaged countries, including Syria and Sudan, has been welcomed by charities and faith leaders.
Dozens more children are expected to arrive this week after a team of British officials were sent to Calais to help French authorities speed up the transfer of minors ahead of the dismantling of the Jungle.
Clare Moseley, founder of refugee support charity Care4Calais, said: "While we are pleased to see the first group of children arriving in the UK, there are still hundreds of unaccompanied and vulnerable young people in the camp facing the fast-approaching demolitions.
"The asylum process has been complicated and slow, it is highly unlikely that all vulnerable camp residents, who have a right to enter the UK, will be processed in time. During the last demolitions 129 children went missing; we cannot let this happen again.
"The speed at which the demolitions have been proposed is a cause for deep concern, and we do not believe the necessary steps to safeguard children and provide the necessary resources for the 10,000 residents to be safely removed from the camp have been taken.
"Care4Calais do not believe demolitions should go ahead until the necessary alternative provisions for refugees are in place, and a long-term solution has been reached."