In a report, Danger Every Step of the Way, released on Tuesday, UNICEF found that 7,009 unaccompanied children made the crossing from North Africa to Italy in the first five months of the year, twice as many as this past year.

“It is a silent and desperate situation – out of sight and out of mind. Yet tens of thousands of children face danger every day and hundreds of thousands more are prepared to risk everything,”

said Marie-Pierre Poirier, UNICEF Special Coordinator for the Refugee and Migrant crisis in Europe. “We urgently need to protect these children from all types of abuse and exploitation by those taking advantage of the situation to exploit their drea”

The report documents the risks that adolescents take in their flight to escape conflict, despair and poverty. Unaccompanied children generally rely on human smugglers, often under a system of 'pay as you go', which opens them to exploitation, UNICEF said.

A total of 2,809 deaths were recorded in the Mediterranean between 1 January and 5 June 2016, as compared with 3,770 for the whole of 2015. The vast majority were on the Central Mediterranean route – and many were children, according to the report.

UNICEF noted that some adolescents are sexually abused and exploited. Italian social workers told the agency that both girls and boys were sexually assaulted and forced into prostitution while in Libya, and that some of the girls were pregnant when they arrived in Italy, having been raped.

However, because of the illicit nature of human smuggling operations, there are no reliable figures to show how many of the refugees and migrants die, disappear into forced labour or prostitution, or linger in detention, UNICEF said.

With summer upon the Mediterranean, the latest numbers of children on the Central Mediterranean route may well be just the tip of the iceberg, according to UNICEF. Another 235,000 migrants are currently in Libya, tens of thousands of them unaccompanied children.

“Every country – those the children leave, those they cross and those in which they seek asylum – has an obligation to establish protection systems focused on the risks that unaccompanied children face,”  Poirier said.

“In the European Union and other destination countries, there is an opportunity for policy and legislative reforms to lead to more opportunities for safe, legal and regular channels for these children,” she added.