Two word-learning experiments were conducted to investigate the understanding of negative sentences in 18- and 24-month-old children. In Experiment 1, after learning that "bamoule" means "penguin" and "pirdaling" means "cartwheeling," 18-month-olds (n = 48) increased their looking times when listening to negative sentences rendered false by their visual context ("Look! It is not a bamoule!" while watching a video showing a penguin cartwheeling); however, they did not change their looking behavior when negative sentences were rendered true by their context ("Look! It is not pirdaling!" while watching a penguin spinning). In Experiment 2, 24-month-olds (n = 48) were first exposed to a teaching phase in which they saw a new cartoon character on a television (e.g., a blue monster). Participants in the affirmative condition listened to sentences like "It's a bamoule!" and participants in the negative condition listened to sentences like "It's not a bamoule!." At test, all participants were asked to find "the bamoule" while viewing two images: the familiar character from the teaching phase versus a novel character (e.g., a red monster). Results showed that participants in the affirmative condition looked more to the familiar character (i.e., they learned the familiar character "was" a bamoule) than participants in the negative condition. Together, these studies provide the first evidence for the understanding of negative sentences during the second year of life. The ability to understand negative sentences so early might support language acquisition, providing infants with a tool to constrain the space of possibilities for word meanings.