Background: The aim of this study is to use an eye tracker to compare the understanding of three forms of implicitness (i.e., presupposition, conversational implicatures, and irony) in 139 pupils from the first to the fifth year of elementary school. Methods: The child was invited to read short texts composed of a context about some characters and a target sentence conveying one of the three kinds of implicitness. After that, there was a comprehension yes/no question to check whether the child had understood the implicit content of the target sentence. At the same time eye, movements were recorded by a remote system (Pro Fusion by Tobii). The number of correct answers, the duration, and the number of fixations on the texts were measured. Results: We showed that children's reading time is positively correlated with the accurate comprehension of implicitness, and that children similarly understand the three types of implicitness. Furthermore, the number and the duration of fixations depend both on the age of the children and on their good or poor understanding of the implicit contents. This fact is particularly noticeable for children in the first-grade class, for whom fixations are significantly longer and more frequent when they correctly understand sentences containing implicitness. Conclusion: These results argue in favor of the possibility of teaching the comprehension of some types of implicitness (presupposition, implicature, and irony) from an early age.