Sleep disturbance is reportedly common after pediatric mTBI. Sleep has been suggested as a predictor of other post-concussive symptoms (PCS) and prolonged recovery. Our objective was to investigate the relation of sleep with PCS in children with mild traumatic brain injury (mTBI) and those with orthopedic injury (OI). Participants were children and adolescents aged 8 to 16 years old diagnosed with either a mTBI (n = 143) or OI (n = 74) who were recruited within 24 hours post-injury after presenting to the Emergency Departments (ED) at Nationwide Children’s Hospital in Columbus, Ohio and Rainbow Babies and Children’s Hospital in Cleveland, Ohio. Parent ratings of child sleep were collected pre-injury (retrospective) and at 3- and 6-months post-injury using the Sleep Disorders Inventory for Students. Symptoms were reported by the child and their parent using the Health and Behaviour Inventory and Post Concussive Symptom Interview. We found that children with mTBI displayed modestly greater, but not statistically significant, post-injury sleep disturbance compared to children with OI. Pre-injury sleep predicted post-injury sleep scores and was also associated with greater PCS regardless of injury Further, children with mTBI who were symptomatic post-acutely based on parent ratings had worse parent-rated sleep outcomes at 3- and 6-months post-injury than did children who were not symptomatic. Further research is warranted to better understand the relationship of sleep and PCS in pediatric mTBI.