Background: Children constitute the main target population for Health Literacy (HL) research. There is limited academic agreement and measurement regarding the knowledge and skills of children concerning making health decisions. Objectives: This review aimed to address this gap of data by providing an outline of current studies of HL in childhood. Moreover, we attempted to comprehend available theories and models concerning the needs and characteristics of children. Methods: Six databases, including Scopus, PubMed, Cumulative Index to Nursing, Educational Resources Information Centre (ERIC), Web of Science, and Allied Health Literatures (CINAHL) were systematically searched using relevant keywords regarding HL and childhood. We included the relevant publications of up to July 2019. Interventional and cross-sectional studies with main focuses on generic HL and relevant content for conceptualizing and defining HL in children were included in this research. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was used to design this review study. Results: Overall, 25 studies conceptualized and defined HL; 8 definitions and 9 models have specifically focused on children aged 3-18 years. HL in children is defined as several main dimensions, each emerging as a collection of related ability, knowledge, and skills that allow an individual to derive at health-promoting actions and decisions, and approach health data, effectively. Conclusions: Identified models and definitions are highly diverse, signifying HL concepts are complex, multidimensional, and constructive. HL has been conceptualized as an action qualification, with the main attention on individual attributes, and understanding its interrelationship with sociocontextual factors. Life phase specialty is mostly conceptualized from disregarding children's specific needs, developmental viewpoint, susceptibilities, and social structures poorly synthesized within most definitions and models.