More than 20,000 of the 31,100 children who reached Europe along mixed migration routes in 2025 arrived without a parent or guardian, according to UN agencies.
A joint report by the International Organization for Migration, International Organization of Migration (IOM), UNHCR and UNICEF found overall child arrivals by sea and land fell 25% from 2024.
The share recorded as unaccompanied, however, rose to 67% from 51% a year earlier, according to the report.
The highest proportions were recorded in Italy and Spain, where 86% of child arrivals were unaccompanied.
IOM Director General Amy Pope warned that limited safe pathways leave children exposed to smugglers, violence and exploitation.
"Children are making difficult and dangerous journeys without a parent or guardian by their side," Pope said, calling for greater cross-border cooperation to protect them.
"No child should have to face these risks alone," she said. "Our shared responsibility is to work across borders to protect them, uphold their rights, and provide the care and support they need."
Among more than 4,600 adolescents and young adults interviewed along Mediterranean, West African Atlantic and Western Balkan routes, nearly half of those asked about their experiences reported physical violence.
On the Central Mediterranean route, 28% said they had been held against their will, while 17% reported being forced to work, according to the report.
Meanwhile, the number of children undergoing refugee resettlement procedures to Europe fell to 3,400 in 2025 from 8,900 a year earlier.
Separately, only 199 children were relocated between European states under the Voluntary Solidarity Mechanism, down 67%, the report said.
None of the relocated children was unaccompanied.
The IOM urged EU 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."
"Unaccompanied and separated children should have immediate access to legal representation," the agency said.