Sensory interests, repetitions, and seeking behaviors (SIRS) are common among children with autism spectrum disorder (ASD) and other developmental disabilities (DD) and involve unusual actions that intensify or reinforce a sensory experience. Researchers and practitioners typically use parent-report measures or informal clinical observations to understand the presence and nature of SIRS. In this study, we used a scoring supplement to the Sensory Processing Assessment for Young Children, an observational measure, to characterize SIRS across three groups of children—those with ASD (n = 40), DD (n = 37), and typical development (n = 39). Group differences were identified in frequency and intensity of overall SIRS, complexity of SIRS, and incidence of particular types of SIRS (i.e., posturing, sighting, proprioceptive seeking, spinning). Facial affect was also explored and found to be primarily neutral during engagement in SIRS across groups. Implications for practice and future research are discussed.