The primary aim of this monocentric randomised controlled study is to evaluate the impact of using GAS to maintain the functional abilities of children and adolescents undergoing TCSE. The secondary aims include evaluating parents' and adolescents' perceived changes in the subject's functional abilities from the moment of stem cell transplantation unit (SCTU) admission to subsequent follow-ups. Another secondary aim is to evaluate the achievement of functional goals as defined by GAS in the experimental group (EG). Other aims include investigating the feasibility of the exercise program and the rehabilitation counselling indications in both groups, as well as the effectiveness of the two interventions and GAS use in the EG.