The South Sudanese government and opposition forces are allegedly recruiting boys as young as 13 to fight in the civil war which has claimed thousands of lives.
According to a recent report by Human Rights Watch (HRW), both warring factions are using child soldiers in combat, which amounts to war crimes when the boys are younger than 15.
The rights group urged President Salva Kiir and his counterpart, former Prime Minister Riek Machar, to stop employing children under 18 and help those already recruited go back home.
"Despite renewed promises by both government and opposition forces that they will stop using child soldiers, both sides continue to recruit and use children in combat," said Daniel Bekele, Africa director at HRW. "In Malakal, government forces are even taking children from right outside the United Nations compound."
HRW's report came a few days after the UN Children's Fund, Unicef, said at least 300 children were released from an armed group in the country.
"For every child released, it's the chance for a new life," said Unicef South Sudan representative Jonathan Veitch. "We are witnessing the negative consequences that being in an armed group has had on the boys; some are withdrawn while others exhibit violent and aggressive behaviour. Instead of playing, they march up and down.
"To avoid the risk of re-recruitment and to ensure that each child can fulfil their potential, they need a protective environment where they not only receive food and water, but also counselling, life skills and the opportunity to go back to school."
Unicef appealed for $13m (£8.5m) to fund the immediate needs of the released children and the vulnerable communities where they live.
The South Sudan conflict erupted in December 2013 when Kiir, from the Dinka ethnic group, accused then vice-president Machar of plotting to overthrow the regime.
The accusations sparked violence in the country, where factions loyal to Kiir and Machar engaged in tit-for-tat violence that has claimed thousands of lives.
At least four million people are also at risk of a man-made famine, due to lack of funds and widespread fighting which has stopped volunteers reaching certain areas.
As the civil war entered its second year in December 2014, human rights activists warned the conflict was far from over and the country has experienced a "colossal loss of life".
At the beginning of February 2015, warring sides agreed on a partial ceasefire with Kiir warning that crucial issues regarding the conflict have not yet been addressed.