As children learn their native languages, they come to have detailed expectations about how to refer to things. These expectations and the detection of their violations are key to inference-making processes. But what do children do when their expectations are not met? Using reaction-time measures and gaze-direction monitoring in a referential communication task, we investigated whether 3- and 5-year-olds notice the infelicity of under- and over-informative utterances and then seek out further information in order to recover the speaker’s intended meaning. We tested how children resolve under-informative instructions such as “Find the orange” when there is more than one orange in view. We also tested whether instructions such as “Find the cat with a tail”, in a context where there is only one, normal-looking cat, would lead them to question why the speaker was over-informative and to seek out further information. Both age groups were sensitive to the ambiguous instructions. Only 5-year-olds were significantly delayed and more likely to check their interlocutor’s gaze when responding to over-informative expressions. We discuss how children’s spontaneous motivation to resolve violations of expectation, coupled with increased speed of linguistic processing, drives language learning.