More than 5,000 refugee children have disappeared without trace this year after arriving in Italy in smugglers' boats from the coast of North Africa, raising fears that they are vulnerable to exploitation and prostitution.
The children are thought to have simply walked out of refugee centres and headed north for richer countries such as the UK, Germany and Sweden, with their journeys sometimes organised by people traffickers.
The migrant children come from countries such as Eritrea, Sudan, Afghanistan and Somalia, which have been ripped apart by war, poverty and political repression.
An estimated 13,000 unaccompanied minors have reached Italy just this year. After being taken to Sicily or the Italian mainland, they set out by train, bus and on foot.
Most were teenagers but some were as young as nine, charity workers said.
The adolescents were the most vulnerable of the 62,000 migrants and refugees who have reached Italy this year. Refugees cannot be detained in migration centres by force so if they want to leave, there is little the Italian authorities can do to stop them.
"Unaccompanied children are at the greatest risk from people traffickers. Some are being forced into manual labour, domestic work, drug smuggling and prostitution," the British charity Save the Children said.
It was crucial that such vulnerable minors were accommodated in safe centres, the charity added, but Italy's migrant reception facilities were overwhelmed with the demand for places.