The number of migrant children who cross the Mediterranean to Italy without parents or relatives doubled to 7,009 between January and May, compared to the same period last year, the UN Children's Fund (UNICEF) reported Tuesday.
More than nine out of 10 underage migrants who have arrived in Italy this year were unaccompanied, according to the UN agency's Geneva office.
Unaccompanied children often rely on people smugglers under a system exposing them to the risk of exploitation, UNICEF warned.
Italian social workers have told UNICEF that boys and girls have been sexually assaulted and forced into prostitution while they wait to make the sea crossing in Libya.
"It is a silent and desperate situation - out of sight and out of mind," said Marie Pierre Poirier, UNICEF's special coordinator for the European migration crisis.
There is currently a surge in young migrants on the central Mediterranean route to Italy because children are trying to join family members who are already in Europe, the International Organization for Migration (IOM) said last week.
UNICEF urged EU countries to allow children to enter the bloc through safe and legal channels, rather than forcing them into the hands of smugglers.
The UN agency criticized that too many children are being held in detention centres due to a lack of facilities catering to children.
In some European countries, children wait up to two years to have their asylum requests processed, the agency reported.