While the Moro Islamic Liberation Front (MILF) leadership has publicly denied using child combatants, evidence recovered from fallen rebel camps indicates otherwise. Witnesses say the MILF has also conscripted children (younger than 18) into "auxiliary roles", such as cooks, porters and guides.
"We could hear the distinct voices of male children screaming amid the din of gunfire," said an army brigade officer in Mindanao, whose unit is in the frontlines against the MILF near the town of Datu Piang, where some of the heaviest fighting has occurred. "This is a condemnable act. They use children to do the fighting, while the MILF leaders hide in the background."
The 12,000-strong MILF has been waging war for an independent Islamic state since 1978 on Mindanao, the mineral-rich southern island, home to four million Muslims. Since the agreement for an autonomous region failed, two senior MILF rebels have cut a deadly swathe across towns and villages, burning down more than 1,000 houses, raiding businesses and killing more than 60 civilians.
Heavy government reprisals have led to many MILF deaths - nearly 200 since August, based on official statistics. About 100,000 civilians are still in evacuation camps, where food shortages and a threat of disease outbreaks amid the monsoon season are straining government resources.
The military is girding for intensified MILF attacks after the Supreme Court on 14 October ruled the deal was "unconstitutional". The 15 justices of the court blasted the government for offering a peace deal that was not publicly scrutinised.
With civilians in many Christian parts of Mindanao also arming themselves against MILF attacks, aid groups say more bloodshed looks inevitable.
Evidence gathered at rebel camps and since declassified by the military showed that children were being used in the fighting. A video clip released to the press by the army showed children in rebel military gear conducting drills in what appeared to be ceremonies inducting them into the movement.
A document left in one of the camps showed "child soldiers" being moulded into "tough, self-reliant fighting men".
The recruits are told to "maintain an aggressive spirit [and instill the] will to close and kill, or capture the enemy", one of the training documents, hand-written in Arabic and broken English, stated. It also contained chapters on how to dismantle and hide automatic rifles and make powerful home-made bombs.
Eid Kabalu, a spokesman for the MILF, told IRIN on 19 October it was against the MILF's policy to recruit children as combatants. He said the allegations were fabrications by the army seeking to discredit the group.
"We deny using child soldiers. These allegations have no basis," Kabalu said, but added that he saw nothing wrong with the MILF taking and caring for children of Muslim parents who may have perished in the fighting. "We take them and try to give them a normal life inside the camps. But we acknowledge that they are in an environment where they are exposed to guns."
He said these children were not forced to become combatants, although they had chores to do around the camp. Kabalu admitted, however, there could be cases where a child inside a camp would later become an MILF fighter. "That is their choice. But to say we recruit children to fight is another thing."
He says under Islamic law, a child who has reached puberty is considered an adult who is given the right to sign legally binding documents, theoretically from the age of 15.
The UN Children's Fund (UNICEF) said in a statement it was highly concerned about the reports of child soldiers, but noted that the Philippines, apart from its domestic laws, was also signatory to international protocols protecting the rights of the child. It said there were enough laws to "advocate for non-recruitment of minors".
"UNICEF considers any person under the age of 18, whether they are involved in or affected by conflict, to be a child. Utmost care should be taken to protect their rights and to secure their return to civilian life. We are concerned how the conflict in Mindanao is affecting children in many ways, including their health, education and their need to be protected from abuse, violence and exploitation."
In a report issued early this year, the London-based Coalition to Stop the Use of Child Soldiers said there were continuing reports that children had joined the MILF in some areas of Mindanao. It said up to 13 percent of MILF fighters in 2005 were children.
"The involvement of children even in auxiliary roles such as cooks, porters, informants and in the case of girl soldiers as sex slaves is a violation of international human rights standards and Philippine laws," Ryan Silverio, the group's Southeast Asia regional coordinator, told IRIN.
Human Rights Watch warned that a sudden escalation of conflict "can lead to a spike in the number of children recruited into armed groups. This is especially a worry when an armed group, like the MILF, is known to use children," said Bedde Sheppard, HRW's Asia researcher on children. Sheppard said the government also needed to "send a strong and clear message to its own armed forces that they too are forbidden from arming, training, or recruiting children".