British and French officials have begun registering unaccompanied children in the Calais "Jungle" who are hoping to join relatives in Britain, reports BBC News.
A significant number of child refugees will arrive in the UK from the migrant camp within days, the BBC understands.
The Children's Commissioner for England has previously said about 300 children in the camp, from countries like Syria and Afghanistan, will come to the UK.
French authorities have said they will close the camp by the end of the year.
It is estimated up to 10,000 people are living in the Jungle which is situated near the port of Calais, and close to the 31-mile Channel Tunnel.
Many of the migrants in northern France attempt to reach the UK by boarding lorries as they approach ports or the Channel Tunnel.
French President François Hollande wants to move the inhabitants it holds to reception centres across the country and demolish the camp.
Aid groups have raised concerns that the planned closure will lead to children disappearing before they are processed.
Home Office officials in Calais have been focusing first on unaccompanied minors who have the right to join relatives under EU legislation.
A separate registration process will take place for vulnerable children who do not have family in the UK.
Under 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 family members living there.
UK law also requires the government to arrange for the transfer to the UK and support of unaccompanied refugee children from Europe.
Home Secretary Amber Rudd has said the government is moving quickly and that she wants as many children as possible brought to the UK before the camp is shut down by the French authorities.
However, the charity Safe Passage, which is working alongside the government, says it has not yet been shown any operational plans setting out how the children will be transferred.
Operations and programme delivery consultant Red Godfrey-Sagoo told the BBC: "There has been a marked increase in activity both from the French authorities and the UK authorities on trying to work out how to get this done quickly. That has been noted.
"Does it mean that we technically have seen any operational plans on how it's going to be delivered? We haven't seen that yet. So we still ask those questions."
She told Radio 4's Today programme she believed the Home Office was working towards taking unaccompanied minors "next week at some point".
Read more of this report from BBC News.
See also: NGOs drop support for 'ill-prepared' Calais Jungle evacuation