The present review aims to provide a comprehensive discussion of the relationship between maternal sign language ability and Deaf children's theory of mind (ToM) development, specifically in Deaf children of hearing parents. Emphasis will be placed on one identified component of ToM, which is called false-belief understanding. Research has recognized the influence of the hearing parent's American Sign Language (ASL) abilities on the Deaf child's own developing ASL and ToM abilities. However, prior research has not provided thorough measurement of hearing parents' ASL abilities, as there has been no measurement of the correctness of the parents' grammatical facial expression while signing. In addition to discussing the progress of ToM research and its subsequent connection to Deaf children's ToM development, the present review will make suggestions to those interested in this area of research.