The average daily amount of physical activity (PA) expended by children in summer camp is unknown. The purpose of this study was to investigate the trends in PA and sedentary behavior in school-aged summer campers during an outdoor adventure summer camp. Participants were a convenience sample of school-aged children (N = 183; 102 males and 81 females; mean age = 9.69 ± 1.47 years) who attended one week of an outdoor adventure summer camp. PA and sedentary behavior were assessed and collected via wrist-worn Actigraph GT3X+ accelerometers during camp hours, from 9am to 4pm daily. Outcome variables included percentage of time spent in sedentary behavior, percentage of time spent in moderate-to-vigorous PA (MVPA), and average steps per day. Data were analyzed using a Multivariate Analysis of Variance (MANOVA) test. Results indicated a decreasing trend of PA across the eight-week summer camp period. Both boys and girls engaged in MVPA for about 9% of the total time during weeks one and two, which decreased to about 7% of the total time by weeks seven and eight. Sedentary behavior remained constant, with an increase during weeks 5 and 6 of camp. Average daily step count decreased by about 3,000 steps per day from the first to the final week of camp. There was a significant main effect for sex on PA (Wilk's [lambda]= 0.000, F = 6.77, p < 0.05) and a significant main effect for week on PA (Wilk's [lambda] = 0.000, F = 3.05, p < 0.05). This indicates the influence of camper sex and week of attendance on PA variables. Overall, weekly PA decreased during the duration of the summer camp. Seasonal outdoor weather patterns and counselor teaching styles may have impacted PA levels of campers. It is recommended that camp staff implement strategies to encourage consistent levels of PA across the summer camp season.