This chapter synthesizes evidence on the prevalence, impacts, and educational inclusion of children with chronic illnesses and developmental disabilities in preschool and elementary years. It documents variable but rising prevalence (with some severe conditions), frequent mental health comorbidity, and disparities by sex and race/ethnicity. While educational support services show mental health benefits, evidence for academic gains remains mixed, particularly for younger children. The chapter advances Response to Intervention and Universal Design for Learning as complementary frameworks to identify needs early, reduce barriers, and deliver tiered, accessible supports. It highlights implementation variability across states, dependence on educator training, and gaps in progress monitoring. Community- and family-centered interventions demonstrate improved caregiver self-efficacy, child quality of life, and family integration, including promising digital and simulation-based approaches. Priorities include stronger causal evidence for early academic outcomes, equity-focused research, and coordinated school–healthcare–family systems to promote inclusion and optimize developmental trajectories.