Four-year-olds were asked to assess an adult listener's knowledge of the location of a hidden sticker after the listener was provided an ambiguous or unambiguous description of the sticker location. When preschoolers possessed private knowledge about the sticker location, the location they chose indicated that they judged a description to be unambiguous even when the message was ambiguous from the listener's perspective. However, measures of implicit awareness (response latencies and eye movement measures) demonstrated that even when preschoolers had private knowledge about the sticker location, ambiguous messages led to more consideration of an alternative location and longer response latencies than unambiguous messages. The findings demonstrate that children show sensitivity to linguistic ambiguity earlier than previously thought and, further, that they can detect linguistic ambiguity in language directed to others even when their own knowledge clarifies the intended meaning.