The current study examined how young children's metacognition-specifically monitoring, control, and metacognitive knowledge-manifests in and contributes to their ultimate problem-solving through question-asking. A total of 101 children (4-6 years of age) participated in a 20-questions-style task in which they were asked to discover the contents of a box by asking questions. Their confidence monitoring regarding their answers, the frequency of different types of questions (i.e., constraint-seeking, confirmation, and ineffective questions), and metacognitive knowledge regarding the question game were measured. The number of correct answers was also recorded. The results indicated that older children exhibited a greater increase in confidence based on the amount of information gained and that their confidence monitoring was more accurate than that of younger children. Older children demonstrated more effective control behaviors, asking more constraint-seeking questions and fewer ineffective questions. The 4-year-olds possessed notable metacognitive knowledge regarding the game, which became more refined with age. In addition to the close relationships among confidence monitoring, control behavior, and metacognitive knowledge, children's sensitive confidence monitoring and use of effective questions predicted the number of correct answers even when age and expressive language were controlled. These findings highlight the development of young children's metacognition and its role in their inquiries and problem-solving abilities.