Robot-assisted rehabilitation is expected to reduce locomotor limitations of children and young adults with Cerebral Palsy (CP). However, to achieve this result, it is essential that the robot is transparent, allowing the user to move freely, and generate joint torques only when the exoskeleton joints significantly deviate from physiological gait patterns. Nevertheless, the development of transparent operation in lower-limb exoskeletons is still an open problem with several implementation challenges. In this study, we implemented a transparent operation strategy on the ExoRoboWalker, an overground exoskeleton designed for children and young adults with CP. The approach employs a feedback zero-torque controller with feedforward compensations for the exoskeleton's dynamics and actuators' impedance. We experimented the proposed system in five healthy subjects walking overground with the exoskeleton in transparent mode (ExoTransp) and non-transparent mode (ExoOff). The proposed transparent controller reduced the user-robot interaction torque and improved user gait kinematics relative to ExoOff. This is a significant step toward an overground gait training exoskeleton for CP population.