There are several neurological disorders that affect the motor development of pediatric patients. These disorders side effects can be treated through robotic rehabilitation devices. Due to the high cost, price and complexity associated to exoskeletons, exosuits have spread along the neurorrehabilitation community. As a consequence, there is a growing need to look for different measurement systems that do not depend on fixed structures or fixed rotation axes. All along this extended abstract, the development of a test bench to validate the knee and ankle flexo-extension measurements taken by three inertial sensors placed on top of the exosuit is covered. Measurements were obtained directly from the comparison of reference and variable inertial sensors; and from a model based on Gaussian Processes. Knee direct measurements were accurate due to the lack of variability, but ankle direct measurements were highly inaccurate, improving considerably with Gaussian Processes.