18 U.S.C. § 2423 : US Code - Section 2423: Transportation of minors

      (a) Transportation With Intent To Engage in Criminal Sexual
    Activity. - A person who knowingly transports an individual who has
    not attained the age of 18 years in interstate or foreign commerce,
    or in any commonwealth, territory or possession of the United
    States, with intent that the individual engage in prostitution, or
    in any sexual activity for which any person can be charged with a
    criminal offense, shall be fined under this title and imprisoned
    not less than 10 years or for life.
      (b) Travel With Intent To Engage in Illicit Sexual Conduct. - A
    person who travels in interstate commerce or travels into the
    United States, or a United States citizen or an alien admitted for
    permanent residence in the United States who travels in foreign
    commerce, for the purpose of engaging in any illicit sexual conduct
    with another person shall be fined under this title or imprisoned
    not more than 30 years, or both.
      (c) Engaging in Illicit Sexual Conduct in Foreign Places. - Any
    United States citizen or alien admitted for permanent residence who
    travels in foreign commerce, and engages in any illicit sexual
    conduct with another person shall be fined under this title or
    imprisoned not more than 30 years, or both.
      (d) Ancillary Offenses. - Whoever, for the purpose of commercial
    advantage or private financial gain, arranges, induces, procures,
    or facilitates the travel of a person knowing that such a person is
    traveling in interstate commerce or foreign commerce for the
    purpose of engaging in illicit sexual conduct shall be fined under
    this title, imprisoned not more than 30 years, or both.
      (e) Attempt and Conspiracy. - Whoever attempts or conspires to
    violate subsection (a), (b), (c), or (d) shall be punishable in the
    same manner as a completed violation of that subsection.
      (f) Definition. - As used in this section, the term "illicit
    sexual conduct" means (1) a sexual act (as defined in section 2246)
    with a person under 18 years of age that would be in violation of
    chapter 109A if the sexual act occurred in the special maritime and
    territorial jurisdiction of the United States; or (2) any
    commercial sex act (as defined in section 1591) with a person under
    18 years of age.
      (g) Defense. - In a prosecution under this section based on
    illicit sexual conduct as defined in subsection (f)(2), it is a
    defense, which the defendant must establish by a preponderance of
    the evidence, that the defendant reasonably believed that the
    person with whom the defendant engaged in the commercial sex act
    had attained the age of 18 years.