1. To determine if treatment with melatonin improves PCS in children following mild traumatic brain injury. Hypothesis: treatment of mTBI children with PCS with 3mg or 10mg of oral melatonin for 28 days will result in a decrease in PCS symptoms as compared with placebo. Effects will be dose-dependent and may be independent of sleep effects. Methods: A randomized double blind, placebo controlled trial (RCT); Outcome measure is a PCS symptom questionnaire. A subsequent RCT will then be performed using the optimal melatonin dose at a second centre.