Introduction Knee injuries are frequent in children, with most studies reporting traumatic knee injuries. Evidence of risk factors for knee injuries in children is sparse. The purpose of this study was to report the extent of traumatic and overuse knee injuries in children and to evaluate intrinsic and extrinsic factors for risk of these injuries. Methods Weekly musculoskeletal pain, sport participation, and sports type were reported by 1326 school children (8-15 yr). Knee injuries were classified as traumatic or overuse. Multinomial logistic regression was used for analyses. Results During the study period, 952 (15% traumatic and 85% overuse) knee injuries were diagnosed. Period prevalence for traumatic and overuse knee injuries were 0.8/1000 and 5.4/1000 sport participations, respectively. Participation in tumbling gymnastics was a risk factor for traumatic knee injuries (OR, 2.14). For overuse knee injuries, intrinsic risk factors were sex (girls OR, 1.38) and previous knee injury (OR, 1.78), whereas participation in soccer (OR, 1.64), handball (OR, 1.95), basket (OR, 2.07), rhythmic (OR, 1.98), and tumbling gymnastics (OR, 1.74) were additional risk factors. For both injury types, sport participation above two times per week increased odds (OR, 1.46-2.40). Conclusions Overuse knee injuries were the most frequent injury type. For traumatic knee injuries, participation in tumbling gymnastics was a risk factor. Risk factors for overuse knee injuries were being a girl; previous knee injury; and participation in soccer, handball, basket, and rhythmic and tumbling gymnastics. Further risk factors for both types of injury were participation in sports above two times per week. Although growth-related overuse knee injuries are a self-limiting condition, a major part of children are affected by these injuries with unknown short- and long-term consequences.