Children and adolescents are not simply small adults. There are important anatomical differences in the structure of growing bone when compared with adult bone. This difference is responsible for most of the differences in injury characteristics seen between these groups.
The most significant differences between musculoskeletal injuries in children and adults are due to the stresses loaded on the epiphyses (separately ossifying ends of the long bones) and the epiphyseal cartilage. Tendons and muscle injuries also differ. Tendons attach to bone via apophyses (which are separate ossification nuclei). Epiphyseal and apophyseal cartilages are potentially weaker than the rest of the skeleton, and the tendons, muscles and ligaments. As a result they are more susceptible to injury. As a result, isolated ligament injuries are unlikely in the paediatric population.
While some of the characteristics of the developing skeleton are more prone to injury there are some things which are relatively protective. For example the articular cartilage layer in children is thicker and has a greater propensity to heal while the metaphysis (long bone) is better able to deform and absorb loads resulting in fewer fractures here.