The report, released Wednesday, details the methods used to recruit the children, the violent acts they are forced under threat to commit and the consequences of their experiences: nightmares, lack of education and illiteracy.
The report and other recent research "has clearly shown that thousands of children are still being recruited - often by force - into state and non-state armies in the region," UNICEF Executive Director Carol Bellamy said in a statement.
The use of child soldiers should be considered "an illegal and morally reprehensible practice that has no place in civilized societies," she said.
UNICEF's study, titled "Adult Wars, Child Soldiers," is based on interviews with 69 current and former child combatants from Cambodia, East Timor, Indonesia, Myanmar, Papua New Guinea and the Philippines.
According to their own accounts, the children suffered brutal training sessions, hard labor and severe punishments, and some saw their own families and friends killed.
Others said they were forced to commit or witness atrocities, including murder and rape. Nearly all those interviewed were given weapons and served in combat. Their average recruitment age was 13.
One soldier, identified as Vasco, said he joined a militia in East Timor for eight months when he was 14.
"When the militia came, my parents were very afraid and said to me, 'If the militia ask you to do anything, just do it or they will kill us,"' the UNICEF report quoted Vasco saying.
"They ordered us to rape," he said. "They beat me with a piece of wood everyday ... I wake up still from bad dreams. I am still constantly afraid."
The youngest of the 67 boys and two girls interviewed was a Myanmar boy, who said he was 7-years-old when recruited by government soldiers promising food and candy. Another boy from Myanmar, who joined the military at age 9, said he was dragged from his house because he was considered an adult.
"It is time for all parties to acknowledge this and work together ... to bring an end to this profound abuse of children's rights," Bellamy said.
The UNICEF study calls for demobilizing all child soldiers; providing support for their reintegration into society, especially through education and vocational training and providing appropriate psychological and social care and support for former combatants.
By Alisa Tang