"They will have endured suffering, including sexual abuse".
An additional 389 children remain in the program, still undergoing rehabilitation.
Among the children to be released today is 15-year-old Victor, who was abducted and forced to be an informant for an armed group for more than a year.
Some children as young as 10 years old have been recruited despite global human rights law prohibiting the use of children under 18 in hostilities.
"Our priority for this group - and for children across South Sudan - is to provide the support they need so they are able to see a more promising future".
David Shearer said the challenge ahead is to ensure the young people have the financial, practical, and emotional support they need to undertake training, find jobs, and access the opportunities they deserve to reach their full potential. We will get them the support they require, so that they have a sense of hope again.
Negotiations to release the children have been carried out by Unicef, state and local authorities, and local groups. They will later undergo medical screening and psychological counseling.
The children were rescued from the Yambio region, the epicenter of fighting in the South Sudanese Civil War that has raged since late 2013, leading to tens of thousands of casualties and over 3.6 million people displaced.
Since the conflict began, 17,000 child soldiers have been conscripted into the conflict, UNICEF reported in March 2017.
Head of UNICEF programmes in South Sudan Mahimbo Mdoe, one of the agencies that helps the children's reintegration prgramme, said not all children were forcibly recruited.
A boy leads other Somali Islamist militia as they patrol the streets of Somalia's capital Mogadishu, August 19, 2009. UNMISS is also progressing other projects to release child soldiers over the coming months in Morobo, Bentiu, and in Pibor where 315 have been verified and registered so far.