After a traumatic event, many children and adolescents develop post-traumatic stress disorder. Studies in adults suggest that emotional reasoning (i.e., drawing conclusions about situations on the basis of one’s emotional responses) is involved in PTSD development or maintenance. This longitudinal study explored whether emotional reasoning predicts children’s PTSD symptoms after a single traumatic event, independently of other risk factors for PTSD, which were subjective trauma severity, anxiety sensitivity, cognitive ability, and neuroticism. Within 3.5 weeks post-trauma, 49 children (7–18 years) completed an emotional reasoning task, questionnaires measuring PTSD symptom severity, subjective trauma severity, anxiety sensitivity, and neuroticism, and a test measuring cognitive ability. About 2.5 months later, 33 children (67 %) completed the PTSD symptom scale again. Results show that emotional reasoning tendency was positively associated with initial PTSD symptoms, particularly avoidance symptoms, and that this was independent of trauma symptom severity, anxiety sensitivity, neuroticism and cognitive ability, but did not predict PTSD symptoms at 2.5 months. This is the first study to our knowledge that examined the relationship between emotional reasoning and PTSD symptoms in children. Findings suggest that emotional reasoning may be involved in the development of PTSD symptoms, but not in their maintenance.