This paper describes some results obtained from analytical three-dimensional motion simulations of child and adult pedestrians impacted by an automobile. The baseline geometric and stiffness parameters used in this simulation correspond to a typical mid-size vehicle, the latter being measured by a dynamic impactor developed for this study. The effects of variation of several of the vehicle's front-end design parameters on the impact severities of a 50th-percentile male adult and a 6-year-old child pedestrian are studied using experimental design techniques. Both the main effects and the first-order interactions among the parameters are investigated, and it is shown that the counter-measure suggested for reducing adult pedestrians' injuries could aggravate child pedestrians' injuries.