Three studies were carried out to investigate sentential complements being the critical device that allows for false-belief understanding in 3- and 4-year-olds (N = 102). Participants across studies accurately gazed in anticipation of a character's mistaken belief in a predictive looking task despite erring on verbal responses for direct false-belief questions. Gaze was independent of complement mastery. These patterns held when other low-verbal false-belief tasks were considered and the predictive looking task was presented as a time-controlled film. While implicit (gaze) knowledge predicted explicit (verbal) false-belief understanding, complement mastery and cognitive flexibility also supported explicit reasoning. Overall, explicit false-belief understanding is complexly underpinned by implicit knowledge and input from higher-order systems of language and executive control.