The current dissertation examines how young children aged from 3 to 6 years come to understand learning from a mentalistic perspective, and how this understanding is related to their own learning. Study 1 found that preschoolers’ prediction of learning is influenced by the informant’s knowledge state, and that there is an age-related increase in the expectation of learning from another and sensitivity to an informant’s knowledge state. Children’s prediction of another’s learning was applied to their actual learning in Study 2, showing that children’s perception of an informant’s knowledge state affects how much information they themselves accept from the informants. Overall, the findings from Studies 1 and 2 demonstrated that children’s judgment of another’s knowledge affects not only their predictions about learning from him, but also their actual learning. Studies 3 and 4 broadened the framework to see how children consider not only the informant’s but also the learner’s mental states. Findings from Studies 3 and 4 indicated that young children come to understand that a person’s knowledge state influences the formation of the intention to learn, and that the judgment of the occurrence of learning requires a change in the learner’s knowledge. Study 5 further examined whether the knowledge-based judgments of another’s learning are applied to judgments of children’s own learning, and whether these judgments are related to how much and how they actually learn. As children judge another’s learning based on the learner’s knowledge, they judged the necessity and desire for their own learning based on their own knowledge state, and they determine whether they have learned based on the presence of knowledge change. Moreover, this knowledge-based reasoning about learning was uniquely related with how much they learned from an example learning situation, and with teacher ratings of their learning related-behavior in schools. The overall findings across five studies indicated that in early childhood, children come to understand learning on the basis of mental states, and that this emerging understanding has important implications for their metacognitive knowledge to regulate their learning as well as their actual learning.