According to the National Institutes of Health, most studies show that short-term melatonin use is safe for kids and produces little to no side effects. (Some lesser-reported side effects include drowsiness, headache, dizziness, or nausea). However, little research has been done about the long-term side effects of melatonin, and because of that, many doctors are wary to recommend melatonin for sleep issues in children.