The present study examines the cognitive activity that is evoked in young children when they are read a picture book that is written for the purpose of teaching mathematics. The focus of this study is to explore the effects of pictures on children's spontaneous mathematical cognitive engagement. The study is based on the assumption that the pictures in a picture book that is aimed at supporting children's learning of mathematics can have story-related components and mathematics-related components. The story-related components of the pictures contribute to grasp the global story context of the text and the mathematics-related components help to understand the mathematical content of the story. All of the pictures of the book under investigation, "Six brave little monkeys in the jungle," have both story-related and mathematics-related components included. The pictures have a representational or an informational function. Four 5-year-old children were read individually the book by one of the authors without any probing. A detailed coding framework was used for analyzing the children's utterances that provided an in-depth picture of the children's cognitive activity. The results show that the picture book as a whole has the potential for cognitively engaging children. However, the pictures with a representational function were found to elicit mathematical thinking to a greater extent than the pictures with an informational function. Moreover, this was found for both types of components included in the pictures. Findings are discussed, practical implications for using picture books in kindergarten are drawn and suggestions for further research are made. (Contains 9 tables and 3 notes.)