This paper examines the relevance of the sentence concept to the understanding of three types of implicitness (presupposition, conversational implicatures, irony). Our experimental protocol involved 105 children (aged 6 to 11) and 82 adults who were asked to read short texts composed of a context about some characters and a target sentence conveying one of the three implicit contents. After reading, children and adults had to answer a comprehension yes-no question and indicate the segments from the text that helped them answer the question. Results showed a difference between the three types of implicitness, with presupposition being detected and understood at a subsentential level, whereas implicatures and irony come under extrasentential level requiring the context to be taken into account. Referring to sentence as a unit of meaning does not seem relevant as soon as understanding is not limited to the literal meaning of what is written, but also concerns what is meant by the text.