Almost 300 South Sudanese child soldiers surrendered their weapons on Tuesday, in the first step of a planned release of 3,000.

The children, aged between 11 and 17, were members of the South Sudan Democratic Army (SSDA) Cobra Faction, according to the UN. Some had been fighting for up to four years.

They laid down their weapons and uniforms during a ceremony held by UNICEF and the South Sudan National Disarmament, Demobilization and Reintegration Commission at the village of Gumuruk in eastern Jonglei State on Tuesday, after their leader signed a peace agreement last year.

"These children have been forced to do and see things no child should ever experience," UNICEF South Sudan Representative Jonathan Veitch said in a press release.

"The release of thousands of children requires a massive response to provide the support and protection these children need to begin rebuilding their lives."

Significant political unrest has plagued South Sudan since its secession from the north in 2011 following two bloody civil wars.

A fresh wave of violence began in December 2013 in Juba, the capital city, after an attempted coup by soldiers loyal to President Salva Kiir's former deputy Riek Machar.

The fighting escalated, spreading throughout the country and fracturing it along ethnic lines, though leaders in South Sudan have stressed that the war is political, not tribal. Described as the "most pressing humanitarian crisis in Africa", the violence has killed more than 10,000 people and displaced 1.9 million. An estimated 12,000 children are thought to have been recruited to fight with armed groups.

UNICEF is now working to reintegrate the released children back into society, as well as reunite them with their families. Partner organisations will also provide healthcare and counselling.

UN Special Representative for Children and Armed Conflict, Leila Zerrougui, said that the release of the child soldiers was "a step in the right direction."

"Helping them take back their lives must be a priority," she said in a statement. "I call on the international community to provide sufficient resources to ensure they have access to the support that will help them heal and return to a peaceful life.

"I urge the Government of South Sudan and the opposition led by Riek Machar to honor their commitments. The release of children in their ranks is long overdue."

South Sudan is one of seven countries highlighed in the UN's 'Children, Not Soldiers' campaign, which aims to put an end to the recruitment and use of children within government forces by 2016.

Around a quarter of a million children around the world are soldiers, and though many are recruited by rebel groups, thousands are part of official government forces. UK charity War Child estimates that 40 per cent of all child soldiers are girls who are regularly subjected to sexual abuse.

Christian charity World Vision is supporting the campaign. "Governments must ensure their military practices explicitly prohibit the recruitment and use of children," senior child rights adviser Erica Hall said last year.

"They must also do everything they can to ensure children are safe and cared for within their own communities, so that joining the military or an armed group is not seen as a better option to their current situation."