Self-help treatments are an important intervention tool, with high accessibility and ease of application. To our knowledge, no research has previously been conducted on any self-help intervention derived from eye movement desensitization and reprocessing (EMDR) therapy. In this study, we evaluated the mental health status of children not directly affected by the pandemic and investigated the effects of using an EMDR-derived self-help intervention in children as a low-intensity treatment. The mental health status of 178 children was evaluated online via the State-Trait Anxiety Inventory for Children (STAIC) and Childhood Posttraumatic Stress Reaction Index (CPTS-RI). Then, children were randomly assigned to intervention and waitlist. A booklet containing EMDR-derived techniques was sent via the school online portal and the intervention was conducted. Posttests were administered 4 weeks later. The attrition rate was 45.5%, with 97 children completing the trial (intervention: 52; waitlist: 45). At baseline, 76.4% of children showed posttraumatic stress symptoms (PTSS) above threshold. Results showed a statistically significant decrease in the posttest PTSS scores for the intervention group compared to waitlist. The intervention group had significant pre–post improvement on all but one subscale, while the waitlist group showed a significant increase in state anxiety on the STAIC. In conclusion, posttraumatic stress was found to be high in children during the COVID-19 outbreak period, and EMDR-derived self-help intervention appeared to be an effective psychosocial intervention tool.