Related Rule
United States of America
Practice Relating to Rule 120. Accommodation for Children Deprived of Their Liberty
The US Field Manual (1956) reproduces Article 76 of the 1949 Geneva Convention IV. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 446.
The US Manual on Detainee Operations (2008) states: “To the extent possible, accommodation must be made for … child detainees.” 
United States, Manual on Detainee Operations, Joint Chiefs of Staff, 30 May 2008, p. IV-4.
The manual also states:
Detainee Categories
The DOD [Department of Defense] definition of the word “detainee” includes any person captured, detained, or otherwise under the control of DOD personnel (military, civilian, or contractor employee) … It does not include persons being held primarily for law enforcement purposes except where the United States is the occupying power …
a. Enemy Combatant. In general, a person engaged in hostilities against the United States or its coalition partners during an armed conflict. The term “enemy combatant” includes both “lawful enemy combatants” and “unlawful enemy combatants.”
b. Enemy Prisoner of War. Individual under the custody and/or control of the DOD according to Articles 4 and 5 of the … [1949 Geneva Convention III].
c. Retained Personnel … Personnel who fall into the following categories: official medical personnel of the armed forces exclusively engaged in the search for, or the collection, transport, or treatment of wounded or sick, or in the prevention of disease, and staff exclusively engaged in the administration of medical units and facilities; chaplains attached to enemy armed forces; staff of national Red Cross Societies and that of other volunteer aid societies duly recognized and authorized by their governments to assist medical service personnel of their own armed forces, provided they are exclusively engaged in the search for, or the collection, transport or treatment of, the wounded or sick, or in the prevention of disease, and provided that the staff of such societies are subject to military laws and regulations.
d. Civilian Internee … A civilian who is interned during an armed conflict, occupation, or other military operation for security reasons, for protection, or because he or she has committed an offense against the detaining power. 
United States, Manual on Detainee Operations, Joint Chiefs of Staff, 30 May 2008, pp. I-3–I-5; see also pp. viii and GL-3.
On 8 May 2006, the US Delegation to the UN Committee Against Torture responded orally to questions regarding US obligations under the 1985 Convention against Torture. On a question concerning juveniles detained at the US naval base in Guantanamo Bay, Cuba, the Legal Adviser to the US Department of Defense responded:
With respect to Madame Belmir’s question about juveniles detained at Guantanamo and the reason for their detention, there are currently no juvenile detainees at Guantanamo … Let me briefly speak about the conditions of detention we provided them while at Guantanamo. After medical tests determined their ages, they were housed in a separate detention facility, separated at a significant distance from the other detainees, and the other detainees were not permitted to have access to them. Indeed, they were housed in a communal facility, rather than cells. They underwent assessments from medical, behavioral, and educational experts to address their needs. Furthermore, we taught them mathematics, English, and reading, and provided daily physical exercise and sports programs.
It is unfortunate that al Qaeda and the Taliban use juveniles as combatants. The United States detains enemy combatants engaged in armed conflict against it and the juveniles were detained to prevent further harm to them and to our forces. 
United States, Department of State, Oral Statements by the United States Delegation to the Committee Against Torture, Geneva, Switzerland, 8 May 2006.