A private key is a referential utterance used to inform selectively. The ambiguity of the utterance conceals meaning from nonselected audience members. The purpose of this study was to examine three aspects of children's understanding of the use of private keys. Experiment 1 concerned children's sensitivity to information in the context of utterance (i.e., the common ground). Experiment 2 examined appreciation of audience design and the speaker's intent. Experiments 3, 4, and 5 explored some reasons for children's problems in understanding private keys. The results show that even first graders are sensitive to common ground information and the speaker's intent. However, audience design is troublesome even for second graders in some situations, probably because they fail to assess the knowledge of the audience members. Private keys are important theoretically because they represent an aspect of referential communication involving the uses of ambiguous utterances that have been ignored by developmental researchers. © 1990.