Children living in refugee camps in northern France are being subjected to sexual exploitation, violence and forced labour on a daily basis, according to the UN children's agency.
A new report by Unicef paints a harrowing picture of abuse, including rape, suffered by unaccompanied children at camps in Calais and Dunkirk.
The report includes cases of children forced to commit crime and of young women being subjected to sexual demands in the slums in exchange for a promise of passage to the UK.
The report has been researched by Unicef France and Unicef UK.
Researchers were told of examples of children being debt slaves and forced into helping human traffickers at ferry terminals.
Passage from France to the UK in the hands of human traffickers can now cost up to £5,500 per person, Unicef said.
The study examined the plight of 60 children aged from 11 to 17 from countries including Afghanistan, Eritrea and Iran, living in camps along the northern French coast between January and April.
Around 30 unaccompanied children at the Calais camp have so far been brought to the UK, Home Office minister Richard Harrington told the Commons this week.
He said he expected the figure to increase "very significantly" as the government attempts to speed up the family reunification process.