Significance: Soccer is one of the most popular sports in the world and participation is rapidly growing in the United States, especially with children. Growing concern exists regarding the rate of head injury among young soccer players. Traditional methods to measure head-ball impact forces during soccer heading require subjects to perform multiple potentially harmful head-ball contacts. The purpose of this study was to design a soccer heading simulation model to safely determine the head impact forces and accelerations experienced by children and to examine how these impacts are affected by ball size, temperature, and pressure. Design: A soccer heading simulation model was formulated using material and inertial properties from anthropometric and head cadaver data. To determine the elasticity of head-ball impacts, coefficients of restitution were determined for a set of soccer balls (sizes 3, 4 and 5) under varying conditions of temperature and ball pressure. Thirty-two male and female players representative of three age groups (under 7, 8 to 11, and 12 to 16 years) were selected for the measurement of soccer ball kicking trajectories and head anthropometry, which served as inputs to the simulation model. Results: Soccer ball coefficients of restitution varied directly with temperature and pressure, and values ranged from 0.76 to 0.80 in the ambient temperature condition. Values were more sensitive to changes in temperature than pressure. Mean peak kicked ball velocities for the ascending age groups were 10.6, 11.8, and 14.1 m/s, and maximum velocities exceeded 18.5 m/s. Heading simulations determined that ball temperature and pressure were inversely related to head-ball impact force and directly related to head acceleration across group and ball size. Simulations of the younger players heading a maximally kicked size 5 ball (e.g. heading an oversized ball) produced impact forces greater than 6 times the respective body weight, and increased head accelerations by 18 to 33% compared with heading the age-rated ball. Results emphasize the importance of using appropriate age-rated soccer balls given that potentially unsafe head impact forces and accelerations may occur when smaller athletes head larger soccer balls. Supervisory personnel (e.g. coaches, athletic trainers) need to be cognizant of sudden drops in temperature, since the accompanying drops in both ball temperature and pressure may increase impact forces realized during heading. The appropriateness of applying established head injury criteria to a young population is also dubious, considering these data are based on an adult population.Keyword(s): athletics/sports, safety/injury prevention, youth sports