Mathematics is one of the key subjects in primary education that provides the foundation for further learning. Introducing innovative methods in the educational process, particularly in the field of teaching and learning mathematics, is important for fostering interactivity and student engagement. CLIL, i.e., Content and Language Integrated Learning, integrates content teaching with foreign language teaching, and is increasingly gaining importance due to its ability to promote multiple linguistic and conceptual understandings. Therefore, in this study, Dr. Seuss’ picture book 123 was used in the 1st grade of primary school within the CLIL method with the common goal of acquiring numbers and learning the English language. This study provides a literature review on the use of matematical picture books and the presence of CLIL method in mathematics teaching. Additionally, an analysis of results of qualitative research is presented with the aim of identifying the advantages and challenges of implementing mathematical picture books within CLIL mathematics teaching. Through this study, an effort has been made to contribute to the discussion on the implementation of the CLIL approach in mathematics teaching and provide useful guidelines for teaching practice in the context of CLIL presence in primary education.