Currently, child seats are widely used as a child restraint system (CRS). The effects of CRS are experimentally investigated according to FMVSS213. In this paper, the dynamic simulation of a child seat is carried out using the LS-DYNA software to develop an advanced CRS. A sled test using an existing child seat is first carried out, and the computer simulations using the LS-DYNA software are compared to the sled test to validate the dummy model and computer simulation. After matching the sled test and computer simulation results of a three-point belt-type child seat, a new type of child seat is developed with the computer simulation and optimization. For weight reduction, an optimization sequence is applied to determine the thickness of each part. For the area of stress concentration, reinforced members are added. The comparison between the simulation and the sled test shows good agreement, and the simulation results are proven useful for the further development of an advanced CRS.