Children exposed to a technological disaster during an understudied part of the lifespan, preschool age and early middle childhood, were assessed in a 5-year follow-up regarding mental health problems, anxiety disorder symptoms, depressive symptoms, physical symptoms, and posttraumatic stress symptoms. Exposed children and their parents (n = 264) reported significantly more problems than controls (n = 515). The differences were greater for conduct problems (including hyperactivity) and physical symptoms, than for anxiety and depression. The long-term effects of a technological disaster on children of pre-school age at exposure appear to differ from those in children, who were victimized at a later age. This may reflect interference with completion of specific developmental tasks.