(a) OFFENSE.-Whoever knowingly- (1) recruits, enlists, or conscripts a person to serve while such person is under 15 years of age in an armed force or group; or (2) uses a person under 15 years of age to participate actively in hostilities; knowing such person is under 15 years of age, shall be punished as provided in subsection (b). (b) PENALTY.-Whoever violates, or attempts or conspires to violate, subsection (a) shall be fined under this title or imprisoned not more than 20 years, or both and