Eleven boys and four girls, some as young as eight and all in apparently good physical condition, were freed from a site in the Occra Hills, 70 miles north-east of the city. All had been behind rebel lines for more than a year.
The children who said they had been fighting alongside rebels were taken to a disarmament camp in Lungi while the others were taken to child care centre.
"Several combatants from different factions have told UNAMSIL they are eager to release all abductees and child soldiers and to enter the [disarmament] programme," the UN mission said.
Eighty-one children have been released so far this year, according to UNAMSIL.