BackgroundThe new Diagnostic and Statistical Manual of Mental Disorders (fifth edition, DSM-5) redefined the boundaries of autism as a spectrum. It has been reported that the number of schoolchildren with undiagnosed developmental disorders (DDs) has risen in Japan. Such children referred to as kininaru-kodomo (KK, “children of concern”) by healthcare professionals fall into a gray area. Therefore, KK are often overlooked at infant medical checkups. This leaves KK without necessary medical care and special needs education. It is urgent to explore the KK concept to enable professionals to properly assess and provide for the healthcare needs of these children at a high risk of DD, ideally with early intervention.MethodsA hybrid model of concept analysis was conducted. Working definitions were obtained from a systematic literature review in the theoretical phase. Subsequent in-depth personal interviews initiated in the fieldwork phase corroborated and refined the concept. These qualitative data were integrated in the final analytical phase to yield the practice-based real definition of KK in clinical settings.ResultsThree themes emerged regarding KK children: children who require special care, children whose special healthcare needs are owing to both individual and environmental factors, and children waiting for the development of a new support system for them or their parents.ConclusionsThis study implies that KK are children who require special support because of individual and environmental factors. The concept of KK is considered useful for keeping children with undiagnosed DDs and/or other healthcare needs connected with support networks. It is strongly recommended that a screening tool be developed that reflects the concept of children at a high risk of DD so that children in this gray area may receive necessary support even before diagnosis.