Virtual Reality (VR) has emerged as a promising tool to support individuals with Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD). Recent advances in artificial intelligence have enabled the integration of virtual agents into immersive environments, yet little synthesis exists on their educational applications. This review analyzes 26 studies to map how virtual agents are designed and implemented in VR contexts for ASD/ADHD populations. Results show that agents most often act as tutors, but also serve as peers, conversational partners, or roleplayers, supporting social communication, emotional learning, daily-living skills, and in some cases academic or vocational training. Interactions were predominantly computer-based or verbal, with limited exploration of immersive multimodal modalities. Most studies targeted children with ASD, while adolescents and adults remain underrepresented.