It has been well-documented that although children around 4 years start to attribute false beliefs to others in classic false-belief tasks, they are still less able to evaluate the truth-value of propositional belief-reporting sentences, especially when belief conflicts with reality. This article investigates whether linguistic cues, verb factivity in particular, can facilitate children's understanding of belief-reporting sentences. Two experiments were implemented, one testing children's knowledge of verb factivity using a gold medal task, and one investigating children's interpretation of belief-reporting sentences using a truth-value-judgment task. Both experiments took advantage of the contrast between neutral non-factive mental verbs and strong negatively biased mental verbs. What sets the two apart is that the complement clause following a strong negatively biased mental verb is definitely false, whereas the one following a neutral non-factive mental verb remains indeterminate in the absence of additional information. The findings were that, first, 4-year-old children were able to tell the difference between the two types of mental verbs in factivity, and second, children's performance was significantly improved when a strong negatively biased mental verb than when a neutral non-factive mental verb was used as the main verb of the belief-reporting sentences. The findings suggest that the use of strong negatively biased mental verbs facilitates children's understanding of belief-reporting sentences. Implications of the findings are discussed in relation to the underlying mechanisms connecting verb factivity and false-belief understanding.