Extremist groups such as the so-called Islamic State are targeting unaccompanied child refugees in conflict zones, a UK think tank warns.
A report from counter-extremism organisation the Quilliam Foundation says smugglers are also being paid to bring the recruits into Europe.
It says that when the unaccompanied under-18s arrive in the UK, hundreds then go missing from the care system.
A new government strategy in May will address some of the concerns, it adds.
The Quilliam Foundation report says groups like IS are active in refugee camps abroad.
They distribute food and try to buy allegiance from desperate youngsters by funding the first leg of their journey to Europe.
“Children and young people who are indoctrinated and recruited by IS are an important resource,” it says.
The foundation’s report says extremists may attempt to infiltrate refugee groups and radicalise young minds at any stage of the trip.
And then when the unaccompanied under-18s reach the UK, hundreds are said to go missing from the care system.
Some run away because they fear not being granted asylum, while others fall victim to abduction, trafficking, sexual and economic exploitation, the foundation says.
Citing figures from 2015, the report says more than 340 children went missing between January and September, with 132 remaining unaccounted for by the end of the year.
According to the report, the government’s forthcoming strategy for safeguarding and promoting the welfare of unaccompanied child refugees is expected to include measures aimed at increasing available foster placements.
It will also include proposals to expand supported accommodation, and reduce the number of unaccompanied children and trafficked children going missing from care.