Related Rule
Practice Relating to Rule 157. Jurisdiction over War Crimes
Poland’s Penal Code (1997) includes a special section on “Offences against peace and humanity, and war crimes” and provides:
Notwithstanding regulations in force in the place of commission of the offence, the Polish penal law shall be applied to a Polish citizen or an alien, with respect to whom no decision on extradition has been taken, in the case of the commission abroad of an offence which the Republic of Poland is obligated to prosecute under international agreements. 
Poland, Penal Code, 1997, Chapter XVIII, Article 113.
In 2009, in its written replies to the Committee on the Rights of the Child concerning its initial report under the 2000 Optional Protocol on the Involvement of Children in Armed Conflict, Poland stated:
Please provide information as to whether Poland assumes extraterritorial jurisdiction over the war crime of conscripting or enlisting children under the age of 15 into the armed forces or using them to participate actively in hostilities. Also in relation to extraterritorial jurisdiction, please indicate whether Polish courts can establish their jurisdiction in case of forced recruitment or involvement in hostilities of a person under 18 if committed outside Poland, by or against a Polish citizen. …
Poland also applies the principle of so-called universal jurisdiction. This principle is reflected in art. 113 of the Penal Code [Pc], that states that regardless of [the] regulations valid … [in the place where the] offence [was] committed, Polish penal law shall apply to … [any] foreigner who … [it has been decided will not] be extradited, in [the event that] … he commits an offence abroad that Poland is obliged to prosecute under international agreements.
In the light of current Polish penal regulations (art. 124 Pc), the forcing – against International law – of persons covered by international protection to join enemy armed forces, is considered a war crime. … In this case, the principle of universal jurisdiction should apply, because Poland is obliged to prosecute this crime by the Geneva Conventions of 1949. The provision in question would only apply to the cases of enlisting the children mentioned in the question, into enemy armed forces. It would not apply to recruitment of persons under 15 to own army. …
Regarding the second part of the question, it should be said that the possibility of exercising jurisdiction by Polish judiciary organs over offences (offences stated in the question included) … results from … [article] 1102 Pc, and the principle of universal jurisdiction. 
Poland, Written replies by the Government of Poland to the Committee on the Rights of the Child concerning the list of issues raised in connection with the initial report of Poland under the Optional Protocol on the Involvement of Children in Armed Conflict, 17 September 2009, UN Doc. CRC/C/OPAC/POL/Q/1/Add.1, § 7.