Safety incidents in children pose a health concern that threatens the lives and the quality of life of children. Indeed, they are the primary cause of child death around the world. Of children’s developmental stages, the preschool age is a critical time when safety incidents occur most frequently and lifelong habits are formed. Medical facilities are supposed to be the safest place for children, but safety incidents among preschool children occur in different ways, including falls, injuries, suffocation, fires, and abductions. Preventing such safety incidents requires education. This study thus aimed to develop a therapeutic play program for preventing safety incidents in preschool-age in-patient children and to check the effects of the program. Developing the program entailed a literature review for selecting and composing the content of therapeutic play. The content was validated by a group of experts before being used in developing a picture book and role play using puppets. To test the effectiveness of the developed program, the study conducted a quasi-experiment by employing a nonequivalent control group pretest-posttest non-synchronized design. The subjects of this study were children aged between 3 and 6 years in the pediatric ward of K General Hospital in Seoul. The study recruited 30 people, including the guardians, for each of the experimental and control groups, and then used their data in the final analysis. Data were collected for about six months from May to November 2021 in the order of pre-test, experimental intervention, and post-test. During the experimental intervention, the researcher provided the control group with one session of general safety education for fall prevention. For the experimental group, the study provided two educational sessions of the developed therapeutic play to individual children: one session of reading the picture book and one session of role play using puppets. The picture books were left next to the children’s hospital bed so that they could read it again anytime. The pre-test and post-test measured the level of knowledge and awareness of safety incidents as well as the child’s safety practice during hospitalization. The pre-test also included items on the general attributes of the children and their guardians. The collected data were analyzed using IBM SPSS Statistics for Windows, Version 27.0. The results of this study are as follows. The finding of the study supported Hypothesis 1: “The experimental group who participated in the therapeutic play for the prevention of safety incidents at hospital will score higher in safety incident knowledge than the control group who did not participate in the therapeutic play” (t = -3.53, p = .001). The findings of this study supported Hypothesis 2: “The experimental group who participated in the therapeutic play for the prevention of safety incidents at hospital will score higher in safety incident awareness than the control group who did not participate” (z = -5.18, p <.001). The findings of this study supported Hypothesis 3: “The experimental group who participated in the therapeutic play for the prevention of safety incidents at hospital will score higher in safety practices than the control group who did not participate” (z = -3.31, p = .001). This study verified that therapeutic play for preventing safety incidents among preschool child in-patients is an effective nursing intervention that improves the knowledge and awareness of safety incidents during hospitalization and the safety practice of hospitalized children. Therefore, the therapeutic play intervention for preventing safety incidents among preschool-age in-patients may be used for handling various types of safety incidents in clinical practice and actively used as a nursing intervention to prevent and manage safety incidents in advance.