Background: The DSM-5 includes a revised definition of the experiences that qualify as potentially traumatic events. This revised definition now offers a clearer and more exclusive definition of what qualifies as a traumatic exposure, but little is known about the revision’s applicability to youth populations. The present study evaluated the predictive utility of the revised DSM definitional boundaries of traumatic exposure in a sample of youth exposed to the 2013 Boston Marathon bombing and related events Methods: Caregivers (N = 460) completed surveys 2 to 6 months postbombing about youth experiences during the events and youth posttraumatic stress (PTS) symptoms Results: Experiencing DSM-5 qualifying traumatic events (DSM-5 QTEs) significantly predicted child PTS symptoms (PTSS), whereas DSM-5 nonqualifying stressful experiences (DSM-5 non-QSEs) did not after accounting for DSM-5 QTEs. Importantly, child age moderated the relationship between DSM-5 QTEs and PTSS such that children 7 and older who experienced DSM-5 QTEs showed greater postbombing PTSS, whereas there was no such relationship in children ages 6 and below Conclusions: Data largely support the revised posttraumatic stress disorder (PTSD) definition of QTEs in older youth, and also highlight the need for further refinement of the QTE definition for children ages 6 and below.