Children with Autism Spectrum Disorder (ASD) frequently rely on Augmentative and Alternative Communication (AAC) systems. Yet, many commercial solutions are hindered by poor usability designs, especially for children with motor and cognitive impairments. This study introduces Hulo Talk, a tablet-based AAC prototype developed using a user-centered, inclusive design approach. A two-phase, mixed-methods study involving 20 children aged 4–18 first evaluated a representative AAC app, Eline Speaks, revealing high error rates and prolonged response times. Based on these findings, Hulo Talk was co-designed with caregivers and tested iteratively to address identified barriers to communication. Within-subject comparisons demonstrated that Hulo Talk significantly reduced task completion times (from 48.0 s to 20.5 s and from 14.2 s to 4.0 s, p < 0.001) and error rates (85% reduction, p < 0.001), while doubling task accuracy across user groups (p < 0.01). Qualitative feedback supported these improvements, citing enhanced usability and reduced cognitive load. These results confirm that accessible, user-driven design enhances AAC system performance for children with complex communication needs, reinforcing the value of inclusive methods in assistive technology development.