Many children with Autism Spectrum Disorder (ASD) exhibit atypical gaze behaviors related to joint attention, a fundamental social-communication skill. Specifically, children with ASD show differences in the skills of gaze sharing and gaze following. In this work we present a novel virtual reality (VR)-based system, called InViRS, in which children with ASD play games allowing them to practice gaze sharing and gaze following. InViRS has three main design contributions: (i) a closed-loop joint attention paradigm with real-time tracking of the participant's eye gaze and game performance measures, (ii) an assistive feedback mechanism that provides guidance and hints in real time, and (iii) a controller that adaptively changes the avatar's gaze prompts according to the performance measures. Results from a pilot study to evaluate the feasibility of InViRS with 9 autistic1 children and 9 typically developing (TD) children offered preliminary support for the feasibility of successful gameplay as well as positive impacts on the targeted skills of gaze sharing and gaze following.