Earlier this year Europol, the EU's law enforcement agency, announced 10,000 children had arrived in Europe, part of the wave of migration that has swept through the continent in recent years. They had been registered and identified. And then they had disappeared. Many of these children are travelling alone. Some are as young as six years old. But the authorities across Europe – the police, the border agencies, NGOs and care organisations – have no idea where they have gone. They are at risk from trafficking and exploitation as well as the hazards of the journey across Europe – jumping onto lorries at Calais, sleeping rough in Northern European weather. Under international and EU law children should be protected. There are various systems and regulations in place to deal with unaccompanied child migrants, whether refugees or not. But the system is failing and children continue to go missing at an alarming rate. Why? (Photo: A young boy walks past the Jungle Books Cafe in the Jungle migrant camp Credit: Christopher Furlong/Getty Images)