Acquired brain damage in children is increasingly frequent, and as main deficit produces motor alterations that manifest as the child grows, affecting muscle tone, coordination and motor control, in order to influence these aspects, fine motor skills are intervened, since these involve a coordinated effort of the brain and muscles, having a direct impact on the learning capacity of children and can improve their independence and autonomy. Although traditional therapies have been proven with great effectiveness, there are also different rehabilitation systems that make use of tracking devices, however not all of them are accessible due to their high cost or the lack of specialists who master them. That is the reason a low-cost optical tracking Controller System is proposed to complement fine motor-oriented rehabilitation, allowing movements to be captured with precision and to obtain feedback on the accuracy of the exercises. In this paper we focus on the first stage referring to the formal specification of the requirements and their validation. The proposal is based on the Leap Motion optical tracking device and limited to exercises with a fine motor and wrist. The controller system aims to provide a better environment for users to run their rehabilitation process, in addition to considering the rehabilitation progress. The proposal uses formal specifications to reduce possible ambiguities in the face of a system that may cause future damage to its users if the rehabilitation is not carried out correctly, in the same way they are used to validate the main properties of the functional requirements. The formal specification language VDM ++ is used to describe the system properties for later modeling and validation through the VDMToolBox tool. As a result, a formal specification of 4 requirements and a 100% coverage analysis were achieved.