Car collisions are, unfortunately, not uncommon and cause 1.35 million deaths each year worldwide. Children are often occupants in cars and to ensure their safety, child restraint systems (CRSs) have been developed. However, CRSs need to be used correctly to be efficient. Several studies, such as field investigations and Q-dummy tests, have shown that a misuse of a CRS can increase the risk of injuries. Typical misuses for a forward-facing CRS and a booster seat, with two real accident parameters, were constructed and simulated using the PIPER child human body model. The kinematics of each case were compared with injury parameters of the head, neck and abdomen. Comparing the parameters to existing injury criteria showed that most of the cases end in AIS3+ head injury, even cases with no misuse. When comparing the results of misuses to the cases where the CRS was correctly used, the dominant result was that misuse resulted in being less effective to protect the child. Moreover, results of chosen misuses compared to Q-dummy tests correlated with their results. Results from this thesis illustrate how important it is for parents to restrain children and route the belt correctly.