The purpose of this study was to improve the conceptual development of an infant through age-appropriate picture books, as well as potentially reveal the effects of such books for developing concepts in children's literature. Study participants used the changing criterion design from single-case research models that consisted of 1 infant and 3 infants between 0-24 months old to ensure the social validity of the study. Age-appropriate informational and fiction picture books were given to the infant observed during the 0-24-month period. The results revealed that the single infant's conceptual knowledge in recipient and expressive language was improved more regularly and systematically compared with age-appropriate picture books under the guidance of parents. These findings provide evidence that infants' conceptual knowledge can be improved through age-appropriate picture books, as well as that both informational and fiction books can be used to effectively expose infants to different concepts. The findings of this study permit the examination of the concept development process in children belonging to different age groups.