At least 117 suicide attacks have been carried out by young people in the Lake Chad basin region since 2014, with nearly 80% of the bombs strapped to girls, a new report says.
UNICEF's Marie-Pierre Poirier said the mere sight of children at checkpoints and markets was sparking fear - meaning almost 1,500 children were detained last year across Nigeria, Cameron, Niger and Chad.
Ms Poirier said: "These children are victims, not perpetrators. Forcing or deceiving them into committing such horrific acts is reprehensible."
The UNICEF report coincides with the third anniversary of the mass abduction of Chibok schoolgirls by Boko Haram, which has pledged allegiance to the Islamic State.
The taking of 276 girls from a boarding school set off an international campaign to find them.
Many of the girls were forced into marriages with fighters and became pregnant.
Dozens escaped, and 21 were freed in October through negotiations with Boko Haram mediated by the Swiss government and the International Committee of the Red Cross.
The government denied a ransom was paid and that it freed some detained Boko Haram fighters in exchange for the girls.
At that time, officials said they were pressing on with negotiations and expected the release of a second group but no more have been freed.
UNICEF said that beyond the high-profile Chibok abductions, the practice of kidnapping children and forcing them to associate with the armed group has been prevalent.
"Young girls are spotted in the markets, and nighttime raids drag them from their beds. In some cases, parents are killed in front of the girls during the process," it said.
"This is typically followed by an extended journey to a Boko Haram base in the forest where the girls are forced into early marriage and sexual slavery."
UNICEF also called for the community reintegration of children who were once under Boko Haram's control, saying many are stigmatized and feared.
A $154m appeal last year for the Lake Chad basin region remains only 40% funded, the agency said.