Children with traumatic brain injury (TBI) are at risk for social impairment. This study aimed to examine social function at 6 months post-TBI and to explore the contribution of injury, cognitive, and environmental influences. The sample included 136 children, 93 survivors of TBI, and 43 healthy controls. TBI participants were recruited on admission and underwent magnetic resonance imaging scan within 8 weeks of injury and behavioral assessment at 6 months post-injury. Healthy controls underwent magnetic resonance imaging scans and behavioral assessment on recruitment. Assessment included parent and child questionnaires tapping social outcome and child-direct testing of cognitive abilities important for social competence (communication, attention/executive function, social cognition). Injury characteristics and environmental measures were collected. At 6-months post-injury, social problems were evident, but not global. Social participation appeared most vulnerable, with more severe injuries leading to greater problems. Greater injury severity and poorer communication skills were associated with poorer social adjustment and social participation, with the impact of family function also significant. Processing speed, younger age, and male gender also contributed to social outcomes. Further follow-up is required to track the recovery of social skills and the changing influences of cognition, brain, and environment over time.