(a) Offense.—Whoever knowingly—
knowing such person is under 15 years of age, shall be punished as provided in subsection (b).
(c) Jurisdiction.—There is jurisdiction over an offense described in subsection (a), and any attempt or conspiracy to commit such offense, if—
the alleged offender is a national of the United States (as defined in section 101(a)(22) of the Immigration and Nationality Act (8 U.S.C. 1101(a)(22))) or an alien lawfully admitted for permanent residence in the United States (as defined in section 101(a)(20) of such Act (8 U.S.C. 1101(a)(20)); 
the alleged offender is present in the United States, irrespective of the nationality of the alleged offender; or
(d) Definitions.—In this section:
(1) Participate actively in hostilities.—The term “participate actively in hostilities” means taking part in—
combat or military activities related to combat, including sabotage and serving as a decoy, a courier, or at a military checkpoint; or