Brain injury induces brain change, which is modulated by sex and developmental age. We examined brain change in juvenile rats after repeated mild brain traumatic injuries. We hypothesized the rat pups would show graded deficits in behavioural performance and a graded increase in protein expression, both increasing with the number of impacts. Three-week-old rats received 1-3 concussions over three days, compared to sham controls without concussive impact. The wire-hanging task revealed a dose-like effect of injury, with performance worsening with the addition of each injury. Glial acidic protein level was highest in the two-injury group. Corticosterone was significantly different for sex and injury status, without an interaction. Our findings suggest repetitive concussion causes rapid changes in motor behaviour and the brain in juvenile rats. Even mild brain injuries require care and attention to avoid repeated injuries and an increase to long-lasting brain disruption.