Preventing Child Exploitation Act of 2018 This bill amends the federal criminal code: to broaden the definition of "illicit sexual conduct" to include conduct involving a minor that would be a sex abuse offense if it occurred inside the United States; to broaden the federal sex offenses that trigger a mandatory life prison term for a defendant with a prior sex offense conviction involving a minor victim; to add violent state crimes to the list of violent offenses that trigger an additional five-year consecutive mandatory minimum prison term for a defendant who fails to comply with sex offender registration requirements and commits such offense; to expand the prior military sex offense convictions that trigger an enhanced mandatory minimum prison term for certain repeat offenses involving a minor; and to revise provisions that prohibit the sexual exploitation of children for the production of child pornography. Adam Walsh Reauthorization Act of 2018 This bill amends the Sex Offender Registration and Notification Act and the federal criminal code: to reauthorize through FY2022 the Sex Offender Management Assistance program; to reauthorize through FY2022 the activites of the U.S. Marshals Service to locate and apprehend sex offenders who violate registration requirements; to reduce the required registration period for certain juvenile delinquent sex offenders who maintain a clean record; to allow states to exempt from public disclosure information about juvenile delinquent sex offenders; to extend the statute of limitations for a minor victim of a federal sex offense to file a civil action; to allow alternative methods for a registered sex offender to comply with the in-person verification requirement; and to limit the aggravated sex abuse offenses that trigger sex offender registration requirements for certain juvenile offenders.