Only this article from September that I can find even mentions the kids.
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...Although AI investigators were unable to determine how many children are imprisoned in Guantanamo Bay, they extracted a statement from Paul Butler, US deputy assistant secretary of defence, who admitted that the military was holding a “very small number” of detainees under the age of 16. He claimed it was “difficult to determine the exact age for the detainees, as birth records are not readily available”.
AI also cites General Richard B. Myers, Chairman of the Joint Chiefs of Staff, who “justifies” this violation of basic rights by declaring, without any evidence, that the children were terrorists. “Despite their age, these are very, very dangerous people,” Myers declared. “They may be juveniles, but they’re not on a little-league team... they’re on a major league team, and it’s a terrorist team.”
Irrespective of the precise age of the children or the allegations against them, it is a criminal offence under international law and the various human rights protocols to hold anyone under the age of 18 as a war prisoner. The US is a signatory to 17 protocols adopted by the Geneva Convention in 1949 to protect children in war zones and other measures established under the United Nations Convention of the Rights of the Child.
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http://www.wsws.org/articles/2003/sep2003/amne-s25.shtml>