More than 20,000 of the 31,100 children who reached Europe along migration routes last year arrived without a parent or guardian, the UN children, migration and refugee agencies said in a joint study.
"This report shows how exposed they are to violence and exploitation when safe pathways are limited and they have to rely on smugglers," said Amy Pope, head of the UN's International Organization for Migration (IOM).
"No child should have to face these risks alone."
While the overall number of children arriving by sea and land in Bulgaria, Cyprus, Greece, Italy, Malta and Spain fell by 25 percent compared with 2024, the proportion of unaccompanied children rose from 51 percent to 67 percent.
More than 12,000 unaccompanied children arrived in Italy, with Egypt, Eritrea, Bangladesh, Somalia and Sudan being the main countries of origin.
And more than 4,700 unaccompanied minors arrived in Spain, chiefly from Algeria, Morocco, Mali and Senegal.
"The journeys are dangerous," the IOM said.
Almost half of migrants aged 15 to 24 that the IOM interviewed said they had suffered physical violence on their journey, particularly in Libya.
"IOM urges European Union member states to put the best interests of the child at the centre of every decision, to guarantee timely access to services, and never to detain children for immigration purposes," the statement said.
