A significant proportion of people worldwide are impacted by the effects of traumatic brain injury (TBI). Research into the incidence and severity of TBI demonstrates that the majority of injuries are mild (such as concussion) and are experienced by children and adolescents. Despite the significance of concussion in young people, there is limited research exploring the impact of this injury on this age group. This is compounded by a lack of clarity on how best to assess concussion symptoms with regard to the measure utilised, timing of assessment, and informant reporting. Assessing concussion in children and adolescents is complicated by the child’s ability to report on concussion symptoms and negotiating reporting from parents and children simultaneously. Previous research has identified gaps in the literature including: lack of acute assessment of symptoms, few longitudinal studies into the pattern of symptom reporting over time, and lack of research associating subjective symptom reports with other objective symptom measures. Therefore, the main aims of this study were: i) To assess parent and child concordance when reporting concussion symptoms over time. ii) To determine the association between parent and child ratings of concussion symptoms and objective symptom measures. This research was part of a wider pilot study, Concussion Recovery and Assessment in New Zealand Adolescents and Children (CRANIAC). It involved 49 pairs of children and their parents or caregivers. Twenty-seven children had sustained a concussion and 22 comprised a comparison group of children with an upper limb injury. The children and their parents completed the Post Concussive Symptom Inventory (PCSI) and Sports Concussion Assessment Tool (SCAT)) on four occasions after injury (one to four days, two weeks, one month, three months). Correlations were used to assess concordance between parent and child ratings at each time point and how the subjective PCSI ratings were associated with the objective symptom assessments from the SCAT. Results showed parents and children from both injury groups reported most symptoms acutely after injury and fewer symptoms at every subsequent time point. There were fewer symptoms recorded and lower agreement for parents/children with an upper limb injury than those with concussion. Parents and children appeared to agree least about symptoms during the acute period of injury and agreement generally strengthened over time as symptom number and severity decreased. Additionally, there was more agreement about the presence or absence of symptoms rather than the severity. Finally, the PCSI ratings from parents or children did not relate to objective SCAT domain measures. This suggests that these scales may be measuring different constructs. In conclusion, symptom report and parent/child concordance for children with concussion is distinct from another injury. When children have sustained a concussion, it is beneficial to obtain reports from the child and a caregiver, particularly closer to injury. This is because parents and children report similar amounts of symptoms but there are discrepancies in the severity and types of symptoms reported by both raters. Therefore, it is not a case of asking who we should listen to, but acknowledging both parents and children give complementary information about concussion. It is especially important to obtain parent and child reports in the acute period after concussion. Similarly, subjective symptom report and objective ratings create a more comprehensive assessment. Future research into parent and child symptom reporting with a larger sample would allow analyses by age group, as well as an analysis of differences between reports. In a broader sense, future research into parent and child agreement across general measures of health and wellbeing may also be beneficial.