Monusco says the children, including 13 girls, had been forcibly recruited in the past six months by the Mai Mai Bakata Katanga militia.
The group is active in Katanga province in the south-east of the country.
Forty of the rescued children have been reunited with their families and the others are said to be receiving care.
Correspondents say the region remains very restive, with local militia demanding a fairer distribution of wealth between the poorer north of Katanga and the southern zone where foreign mining firms operate.
Monusco – the UN’s stabilisation mission in DR Congo – said in a statement that the children had been identified and separated from the militia through the concerted efforts of child protection agencies.
“We are extremely concerned by continued reports of active recruitment by Mai Mai Bakata Katanga and other armed groups in eastern DRC,” said Monusco head Martin Kobler.
“Children face unacceptable risks when they are recruited for military purposes. 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 said that since the beginning of the year, 163 children, including 22 girls, have been removed from the militia.