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.