The Mayi Mayi Bakata Katanga armed militia had recruited the children, ages 8 to 17, during the past six months, the U.N. group said in a statement Friday.
Forty of the children were immediately reunited with their families. The rest are in the custody of child protections agencies until their parents can be notified.
The child protection agencies had worked together in several areas of Katanga Province to identify and separate the children, the statement said.
Martin Kobler, head of the U.N. Organization Stabilization Mission in the Democratic Republic of Congo, said his organization was "extremely concerned by continued reports of active recruitment" of children by Mayi Mayi Bakata Katanga and other armed groups.
"Children face unacceptable risks when they are recruited for military purposes," Kobler said. "The recruitment of children, particularly those under 15 years of age, could constitute a war crime and those responsible must be held to account."
MONUSCO and partnering child welfare groups have separated 163 children, including 22 girls, from the armed group since the first of the year.