March 24, 2017 0201 GMT
UNICEF said almost 26,000 children – most of them unaccompanied – crossed the Mediterranean last year, BBC reported.
In its new report, UNICEF said many children suffer from violence and sexual abuse at the hands of smugglers and traffickers.
But they rarely report their abuse, for fear of arrest and deportation.
The agency also said there is a lack of food, water and medical care in Libya's detention centers.
The plight of children, many of them unaccompanied by parents, has become a tragically familiar part of the wider story of mass migration over the past two years.
But while much has been said about the extreme dangers faced at sea, the privations experienced on land, especially in Libya, are less familiar.
UNICEF’s latest report, “A Deadly Journey for Children,” documents – in sometimes horrific detail – stories of slavery, violence and sexual abuse experienced by huge numbers of vulnerable children making their perilous way to Italy.
“What really shocked UNICEF staff and me... is what happens to them [children] on this route,” said Justin Forsyth, the organization’s deputy executive director. “Many of these children have been brutalized, raped, killed on this route.”
Much of the violence is gratuitous, and much of it is sexual.
"Nearly half the women and children interviewed had experienced sexual abuse during migration," the report said. "Often multiple times and in multiple locations."
Borders, it seems, are particularly dangerous.
Many of the assailants are in uniform. This is said to be just one reason why those who suffer abuse are reluctant to report their experiences.
And Libya, as the funnel through which so many journeys pass, has earned itself a shocking reputation as the epicenter of abuse.
The report maps 34 known detention centers in Libya, three of them deep in the country's desert interior.
Most are run by the government's Department for Combating Illegal Migration. But UNICEF says that armed groups also hold migrants in an unknown number of unofficial camps.
In 2016, more than 180,000 migrants crossed from Libya to Italy. According to the UN, almost 26,000 of these were children, most of them unaccompanied. The number of unaccompanied children appears to be soaring.