Nigeria's army said three child suicide bombers set off explosions that killed six others and injured at least 24 people.
Army spokesman Colonel Sani Kukasheka Usman said on Monday that the children were between the ages of 10 and 15 years.
He said they attacked a security checkpoint in Benisheikh, a town in Nigeria's northeast Borno State.
Usman said the army on Sunday killed at least 12 Boko Haram fighters in an operation in the same state and added that they raided two camps in the operation.
Boko Haram's six-year-old Islamic uprising has killed an estimated 20,000 people and driven 2.3 million from their homes, according to Amnesty International and the United Nations.