Objectives: A notable minority of children will experience persistent post-concussive symptoms (PCS) following mild traumatic brain injury (mTBI), likely maintained by a combination of injury and non-injury related factors. Adopting a prospective longitudinal design, this study aimed to investigate the relative influence of child, family, and injury factors on both acute and persistent PCS in young children. Methods: Participants were 101 children aged 2–12 who presented to an Emergency Department, with either mTBI or minor bodily trauma (control). PCS were assessed at time of injury, 1 week, and 1, 2, and 3 months post-injury. Predictors included injury and demographic variables, premorbid child behavior, sleep hygiene, and parental stress. Random effects ordinal logistic regression models were used to analyze the relative influence of these predictors on PCS at early (acute – 1 week) and late (1–3 month) post-injury phases. Results: Presence of mTBI was a stronger predictor of PCS in the early [odds ratio (OR)=18.2] compared with late (OR=7.3) post-injury phase. Older age at injury and pre-existing learning difficulties were significant predictors of PCS beyond 1 month post-injury. Family factors, including higher levels of parental stress, higher socio-economic status, and being of Anglo-Saxon descent, consistently predicted greater PCS. Conclusions: Injury characteristics were significantly associated with PCS for 3 months following mTBI but the association weakened over time. On the other hand, pre-existing child and family factors displayed an increasingly strong association with PCS over time. Follow-up for these “at-risk” children which also addresses family stress may minimize longer-term complications. (JINS, 2016, 22, 793–803)