The children (and wives) of foreign ISIS fighters 73 fighters.17 Notably, membership in a terrorist organization is a concept that is prone to different (and sometimes questionable) interpretations at the domestic level, and for which no definition is provided at the international or regional levels.18 With regard to FTFs and their family members, especially young children who most certainly did not choose to become part of ISIS, affiliation with or membership in a terrorist organization cannot constitute legitimate grounds for indefinite deprivation of liberty and conviction without any evidence.19 In fact, any law that criminalizes and sanctions material support and association with terrorists has to comply with the requirements of legality and judicial guarantees, and, in the case of children, detention and prosecution must always be seen as measures of last resort. 20 In light of these preliminary considerations, the present article aims at clarifying which specific issues emerge in relation to FTFs’ accompanying family members and at investigating the current situation through the lenses of international law. Reference will be made in particular to international humanitarian law, international counter-terrorism law, the law of diplomatic and consular relations and international human rights law, in order to determine, first, whether States of nationality have an 17 The difference is utterly important, as the present author has explained elsewhere ‘[i]n most countries fighting abroad does not automatically amount to an offence. Foreigners may face criminal charges for participating in a non-international armed conflict because they do not enjoy combatant status; or they can be charged if a national law makes it illegal to enlist in a foreign army at war with a State at peace with their country of origin’. Capone (n 11) 229. 18 Council Directive (EU) 2017/541 of 15 March 2017 on combating terrorism and replacing Council Framework Decision 2002/475/JHA and amending Council Decision 2005/671/JHA [2017] OJ L88/6, art 2(3): ‘“terrorist group” means a structured group of more than two persons, established for a period of time and acting in concert to commit terrorist offences; “structured group” means a group that is not randomly formed for the immediate commission of an offence and that does not need to have formally defined roles for its members, continuity of its membership or a developed structure’ (emphasis added). 19 ‘“Everyone Must Confess”. Abuses against Children Suspected of ISIS Affiliation in Iraq’ Human Rights Watch (6 March 2019) 15-10 <www.hrw.org/sites/default/ files/report_pdf/iraq0319_web_1.pdf>. 20 ‘Protection of Human Rights and Fundamental Freedoms while Countering Terrorism, Note by the Secretary-General’ UN Doc A/64/211 (3 August 2009) para 53. See also N Quénivet, ‘Does and Should International Law Prohibit the Prosecution of Children for War Crimes?’ (2017) 28 EJIL 433, 451-453; ‘UN Standard Minimum Rules for the Administration of Juvenile Justice’ (Beijing Rules), UNGA Res 44/33 (29 November 1985).