Related Rule
Germany
Practice Relating to Rule 120. Accommodation for Children Deprived of Their Liberty
Germany’s Military Manual (1992) provides: “The detaining power shall ensure that members of the same family are lodged together in the same place of internment.” 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 593.
In 2005, in its Seventh Human Rights Policy Report, Germany’s Federal Government reported to the Bundestag (Lower House of Parliament):
With the 1998 guidelines on the handling of crises related to internally displaced persons (“Guiding Principles on Internal Displacement”) by the then Representative of the UN Secretary-General on the Human Rights of Internally Displaced Persons, Francis Deng, the international community has a practice-oriented document, which summarizes existing standards on the protection of internally displaced persons and gives further recommendations. Although these guiding principles are not a binding instrument under international law, their acceptance by States, international organizations and NGOs has continued to grow over the past years, so that now they are virtually regarded as customary international law. 
Germany, Federal Government, Seventh Human Rights Policy Report, 17 June 2005, pp. 97–98.
In 2010, in reply to a Minor Interpellation in the Bundestag (Lower House of Parliament) entitled “Treatment of child soldiers by the German armed forces (Bundeswehr) during operations abroad”, Germany’s Federal Government wrote:
8. Which procedures are envisaged for the treatment of child soldiers injured, apprehended or detained by the Bundeswehr?
In the completed operation EUFOR RD CONGO, the following framework was adopted regarding apprehended or detained children and included in the pocket card of June 2006 for the German contingent of the operation EUFOR RD CONGO:
c) If feasible, they are to be accommodated separately from other detainees. If they are detained together with family members, they must be accommodated together with these family members. 
Germany, Lower House of Federal Parliament (Bundestag), Reply by the Federal Government to the Minor Interpellation by Members Paul Schäfer, Jan van Aken, Sevim Dağdelen, further Members and the Parliamentary Group DIE LINKE, BT-Drs. 17/2998, 21 September 2010, pp. 4–5.
The Federal Government also wrote:
19. In the course of ISAF [International Security Assistance Force] and OEF (Operation Enduring Freedom), was there an agreement on special procedures for dealing with child soldiers?
a) If so, which ones?
b) If not, why was this considered not to be necessary?
The Bundeswehr does not contribute forces to Operation Enduring Freedom (OEF).
Within ISAF, the ISAF rules inter alia contain the following provisions on the potential detention of minors:
To the extent possible, detained persons are to be accommodated separately, based inter alia on age; joint accommodation of family or clan members should be made possible. 
Germany, Lower House of Federal Parliament (Bundestag), Reply by the Federal Government to the Minor Interpellation by Members Paul Schäfer, Jan van Aken, Sevim Dağdelen, further Members and the Parliamentary Group DIE LINKE, BT-Drs. 17/2998, 21 September 2010, p. 7.