Objective: The purpose of this study is to identify research trends in studies on mixed-age classroom in kindergartens and childcare centers published in Korean academic journals, focusing on keywords and research topics. It also aims to derive implications and future directions for research on mixed-age classrooms. Methods: A systematic literature review was conducted on journal articles related to mixed-age classrooms in early childhood education published between 1990 and 2025. A total of 77 articles were selected for analysis. The abstracts of the selected articles were used as text data to extract 30 core keywords, which were then visualized using a word cloud. In addition, topic modeling based on the Latent Dirichlet Allocation (LDA) algorithm was employed to structurally examine research trends. Results: First, the keyword analysis indicated that studies on mixed-age classrooms relatively frequently focused on keywords such as teachers, play, peers, kindergarten, and art. Second, the topic modeling analysis revealed that research on mixed-age classrooms in early childhood education settings has been conducted mainly around three themes: play and interaction, social relationship experiences, and art activities and emotional expression. Conclusion: To expand the philosophical, theoretical, and practical horizons of research on mixed-age classrooms, this study proposes several directions for future research. First, the meaning of mixed-age classrooms should be reinterpreted from a post-reconceptualist perspective. Second, research exploring generative curriculum models for mixed-age classrooms should be further developed. Third, more practical cases that expand the range of age compositions in mixed-age classrooms should be reported. Finally, the educational implications of mixed-age classrooms should be critically discussed within broader macro-level contexts, including declining birth rates, changes in social structures, and policies related to integrate early childhood education and care.