Previous studies demonstrated that dual-task impairments are higher in children than in young adults. A previous study systematically assessed the sources of these larger dual-task impairments by identifying age-related differences in capacity limitations during dual-task processing. Capacity limitations in central cognitive processes were present in both age groups, while perceptual capacity limitations were larger in children than in young adults. However, the literature lacks further confirmations and explanations for increased dual-task impairments in children. Moreover, this previous study was not informative regarding age-related differences in potential capacity limitations during central cognitive processing in relation to limitations during motor processing. Therefore, in a German context, the present study investigated children (N = 32) and young adults (N = 32) by combining visual (Task 1) and auditory (Task 2) sensorimotor tasks, separated by a varying stimulus onset asynchrony, in dual tasks of the psychological refractory period (PRP) type. Performance differences were assessed by manipulations of task difficulty in Task 1. The results replicated the finding of increased dual-task impairments in children compared with young adults. Furthermore, the manipulations in the PRP dual task resulted in similar effects in both age groups. Thus, these findings confirmed the presence of capacity limitations during central cognitive processing, while there were no processing limitations in motor processing between children and young adults.