Atypical sensory response patterns are common in children with autism and developmental delay. Expanding on previous work, this observational electroencephalogram study assessed auditory event-related potentials and their associations with clinically evaluated sensory response patterns in children with autism spectrum disorder (n = 28), developmental delay (n = 17), and typical development (n = 39). Attention-orienting P3a responses were attenuated in autism spectrum disorder relative to both developmental delay and typical development, but early sensory N2 responses were attenuated in both autism spectrum disorder and developmental delay relative to typical development. Attenuated event-related potentials involving N2 or P3a components, or a P1 × N2 interaction, were related to more severe hyporesponsive or sensory-seeking response patterns across children with autism spectrum disorder and developmental delay. Thus, although attentional disruptions may be unique to autism spectrum disorder, sensory disruptions appear across developmental delay and are associated with atypical sensory behaviors.