This study examined the effects of micronutrients on children with clinically elevated stress and anxiety 23–36 months after experiencing a natural disaster (a major earthquake). A single-case multiple-baseline design allocated 14 children (7 males, 7 females; aged 8–11 years; 10 with formal anxiety-disorder diagnoses) randomly to 1, 2 or 3 week baselines. Participants then took eight capsules/day of a micronutrient formula (EMPowerplus) during an 8-week open-label trial. Assessment instruments were the Children’s Global Assessment Scale (CGAS), the Screen for Child Anxiety-Related Emotional Disorders (SCARED), the Pediatric Emotional Distress Scale (PEDS), and the Revised Children’s Manifest Anxiety Scale (RCMAS). Symptom severity declined slightly in baseline for some children and declined much more during intervention for all children. Effect sizes at end of treatment were −1.40 (RCMAS), −1.92 (SCARED), +1.96 (CGAS), and −2.13 (PEDS). Modified Brinley plots revealed decreases in anxiety and improvements in overall functioning for 10 out of 11 completing participants. Side effects were mild and transient. The study provided evidence that treatment with a dietary supplement containing micronutrients reduced children’s post-disaster anxiety to a clinically significant degree. Future placebo-controlled randomized-controlled trials and treatment-comparison research is recommended to determine if this is true of anxiety in general.