The aim of this paper was to provide an overview of research focused on the assessment and significance of fat mass in early childhood and preschool-aged children. The content analysis method was employed in the research. An electronic literature search was conducted in the PUBMED database. The search included relevant English-language papers published up until June 12, 2024. The systematic search involved three key criteria: (1) the keyword "fat mass in preschool children"; (2) the time frame within which the paper was published—the last five years; (3) fully accessible papers in English related to the subject of the research. A total of 54 papers that met the established criteria were found. The data were processed using Microsoft Excel (Office, 2019) and presented in the form of tables and charts. The results showed that the most commonly used methods for assessing children's fat mass were air displacement plethysmography, bioelectrical impedance analysis, and anthropometry. Most of the studies focused on examining fat mass in preschool-aged children, while early childhood was less frequently researched. Furthermore, the areas of interest in recent studies on children's fat mass were diverse, with nutrition standing out, indirectly emphasizing its important role in regulating fat mass in children.