The Colombian rebel group, the Farc, has handed over a first group of child soldiers as part of a peace accord signed with the government last month.
The International Red Cross said the eight children would be given mental and physical examinations before being taken to temporary reception centres.
They said the ultimate aim was to try to return the young people to their families.
The Farc says it has 21 soldiers under 15 years of age.
The Colombian defence ministry has put the figure for those under 18 far higher.
Colombia's High Commissioner for Peace, Sergio Jaramillo, said "They are going to gradually leave the camps in different regions of the country."
"It's not going to be all at once -- it is a process and this is the first phase."
To respect the young people's privacy, the location of the handover and their ages have been kept secret.
Last February, the Farc announced it would raise the age of recruitment to 18.
Three months later, in May, the Farc and the government announced all under-18 combatants would be leaving rebel camps.
Colombian army sources estimate that close to half of all Farc members were recruited as children.
The Farc has long been accused of forcing children to join its ranks - a human rights violation - as a way to demonstrate its military strength in rural areas where it is dominant.
Many young soldiers say they joined the Farc of their own free will to flee poverty or domestic violence.
More than 220,000 people have been killed in almost 52 years of armed conflict in Colombia and more than six million people have been internally displaced.
Colombians are set to vote on the ratification of the peace plan in October.