To describe the walking performance and physical activity of children with cerebral palsy (CP) by Gross Motor Function Classification System (GMFCS) level, age, sex, and geographical location; and, to examine the concurrent validity of the 4-item Early Activity Scale for Endurance (EASE) to walking performance and physical activity scores. Seventy-nine children with CP participated. Parents completed the 4-item EASE. All children wore an Actigraph monitor (n = 79), and children in GMFCS levels I - III also wore a StepWatch monitor (n = 50), for seven days. Only GMFCS level yielded significant differences in average strides taken per day, in strides per day taken faster than 30 strides per minute, in average physical activity counts per minute, and in minutes per day spent in moderate to vigorous physical activity. The 4-item EASE findings were moderately correlated with average physical activity counts per minute (.61, p< .001) and minutes per day spent in moderate to vigorous physical activity (.62, p < .001). GMFCS level is predictive of both walking performance and physical activity in children with CP. The 4-item EASE may provide a quick and valid way to monitor physical activity in children with CP.