Introduction Traumatic brain injury (TBI) is the main cause of death in children around the world. The last Dutch epidemiological study described the incidence over 10 years ago. Mechanism of injury seems to change with the age of the child, therefore it is important to appreciate different age groups. To be able to lower the impact of childhood TBI, an understanding of current incidence, mechanism of injury and outcome is necessary. Methods A nationwide retrospective cohort study was conducted. The Dutch National Trauma Database was used to identify all patients 18 years and younger who were admitted to a Dutch hospital with moderate-severe TBI (Abbreviated Injury Score≥3) in the Netherlands, from January 2015 until December 2017. Subanalyses were done for different age groups. Results In total, 1413 patients were included, of whom 5% died. The incidence rate of moderate-severe TBI was 14/100,000 person years. Median age was 10.4 years. Largest age group was patients <5 years, incidence rate was highest in patients ≥16 years. Falls were more common than road traffic accidents (RTA), but RTAs occurred far more frequently amongst children over 10. RTAs predominantly consisted of bicycle accidents. Mortality rates increased from youngest to oldest age groups, as did the chances of a Glasgow Outcome Scale score of 3. Conclusion Paediatric moderate-severe TBI represents a significant problem in the Netherlands. Falls are the most common mechanism of injury amongst younger children and RTAs amongst older children. Unique for the Netherlands is the vast amount of bicycle accident related injuries.