Is children's literature only beneficial to children? Or do the benefits of children's literature also extend to the knowledge and mathematical skills of the teachers who employ it and reflect on it? This study seeks to investigate the role of picturebooks on the mathematical knowledge of preschool teacher candidates. For this purpose, in-depth examinations of how picturebooks can be used in teaching preschool mathematics and children's literature. As well as the changes in the content knowledge of the teacher candidates, were done by conducting focus group interviews with teacher candidates. This is a qualitative case study consisting of focus group discussions in which high-level knowledge sharing and production can be achieved through interaction and associations. In the research, 11 picturebooks were discussed, and 8 teacher candidates participated in 6 focus group interviews lasting a total of 338 min throughout a 7 week period. The study's findings have demonstrated that through children's literature, teacher candidates' misconceptions about measuring length can be revealed and eliminated without the need for another source, with discussions based on consciously and systematically selected picturebooks. Thus, it can be said that picturebooks act as a catalyst for the studies that aim to enhance the mathematical content knowledge of teacher candidates. The study has also observed that picturebooks can comprehensively address the fundamental concepts of length measurement.