In this paper, we describe the co-design process for creating interactive pediatric physical therapy (PT) spaces by applying gamification techniques, with a focus on helping children with gross motor delay which impact their mobility, independence, quality of movement, and balance coordination. The co-design of activities for age-appropriate gross motor skills was conducted through iterative cycles of co-creation with physical therapists and occupational therapists. Consequently, we propose exergaming interactive user interfaces, designed in a way to support improving a child’s gross motor performance. The design involves personalized illustrative graphic characters drawn on the room’s surfaces. The efficacy of such immersive space will be examined in experimental user acceptance studies and the design implications will be discussed.