We studied the effect of two social settings (collaborative versus competitive) on the visual and auditory expressions of uncertainty by children in two age groups (8 and 11). We conducted an experiment in which children played a quiz game in pairs. They either had to collaborate or compete with each other. We found that the Feeling-of-Knowing of eight-year-old children did not seem to be affected by the social setting, contrary to the Feeling-of-Knowing of 11-year-old children. In addition, we labelled children’s expressions in clips taken from the experiment for various visual and auditory features. We found that children used some of these features to signal uncertainty and that older children exhibited clearer cues than younger children. In a subsequent perception test, adults rated children’s certainty in clips used for labelling. It appeared that older children and children in competition expressed their confidence level more clearly than younger children and children in collaboration.