Children with developmental disabilities such as autistic spectrum disorder have a high possibility of showing atypical sensorial characteristics. Schools and after-school facilities should provide a learning and living environment for these children. However, the current environment is unsuitable because it is too noisy for children with hypersensitivity. In this study, we developed a spatial setting that considers the atypical auditory characteristics of children with developmental disabilities to improve their comfort by adjusting the sound environment in an afterschool day service facility. First, we measured the sound environment, observed activities of children, and conducted interviews of the support staff of the facility. Based on the problem and requirements indicated by the survey, we installed a spatial setting. It consisted of small boxes with sound-absorbing materials attached inside to allow a child to place his/her head or whole body and take rest in a quiet environment. It also included a foldable partition, tent, and curtain made of sound-absorbing fabrics. This spatial setting functions as a place for children to escape from environmental stimuli, calm down, and change their feelings. According to the support staff, this setting is also effective for processing auditory information, improving concentration, and facilitating communication.