Children tend to select a novel object rather than a familiar object when asked to identify the referent of a novel label. Current accounts of this so-called "disambiguation effect" do not address whether children have a general metacognitive representation of this way of determining the reference of novel labels. In two experiments (each N = 48), three- and four-year-olds received a prediction task that required such a representation. In the initial phase, children completed four disambiguation test trials that were presented as instances of the same "game." In the next phase, they received four additional trials. These differed only in that before the label was presented, children were asked to predict which object "was going to be right." On the first prediction trial, most four-year-olds predicted the novel object, whereas most three-year-olds did not. On subsequent trials, despite having received feedback regarding predictions, three-year-olds showed no tendency to begin to predict the novel object, whereas most four-year-olds continued to make this prediction. These findings add to the evidence that most children develop a general metacognitive representation of their tendency to map novel labels onto novel rather than familiar objects some time around their fourth birthday.