The biomechanical characteristics of children and adults differ greatly, because children are not just small adults. This applies to the body proportions as well as to the strength of bones, muscles, and ligaments. While the head size at the time of birth is approximately a quarter of the body size, this ratio decreases to one-seventh for adult humans.
Add to this the fact that the strength of the neck muscles increases as the child develops. The neck muscles of a baby are not yet sufficiently developed to stabilize the proportionally larger head. This biomechanical peculiarity is the reason why babies are transported most safely in a rear-facing baby seat. In comparison to the skull of an adult, the skull of an infant is less resistant to impact trauma. The bones of small children are softer and more flexible, and not all skull bones have already grown together firmly.
Also, the ribs of small children are more elastic than those of adults. Therefore, an impact causes more deformation of the ribs, which makes it easier for the organs inside to be injured. In addition, the chest and pelvis are smaller and thus the organs in the abdomen are less protected by the rib cage and pelvis.