About 80 children rescued from a Boko Haram camp in Cameroon cannot remember their own names or origins, according to an aid official who visited them.
The children - aged between 5 and 18 - did not speak English, French or any local languages, says Christopher Fomunyoh, a director for the US-based National Democratic Institute (NDI).
The children were found at a camp in northern Cameroon in November.
Nigeria-based Boko Haram militants have extended their campaign into Cameroon.
The militants are fighting to establish an Islamic caliphate in north-eastern Nigeria.
They control several towns and villages in the region and recently pledged allegiance to Islamic State (IS) militants, who have seized large areas of Syria and Iraq.
The children were rescued in Cameroon after security forces - acting on a tip-off - raided what was thought to have been a Koranic school.
Mr Fomunyoh told the BBC's Randy Joe Sa'ah in Yaounde that he had visited an orphanage that was helping rehabilitate the children.
He said the children had spent so long with their captors, being indoctrinated in jihadist ideology, that they had lost track of who they were.
"They've lost touch with their parents," he said. "They've lost touch with people in their villages, they're not able to articulate, to help trace their relationships, they can't even tell you what their names are."
Meanwhile, a suspected Boko Haram attack on Tuesday killed at least six people at a marketplace in the northern Nigerian town of Maiduguri.
The suicide bombing was reportedly carried out by a middle-aged woman.
Boko Haram at a glance
Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009 to create Islamic state
- Thousands killed, mostly in north-eastern Nigeria - has also attacked police and UN headquarters in capital, Abuja
- Abducted hundreds, including at least 200 schoolgirls
- Controls several north-eastern towns
- Launched attacks on neighbouring states