What is the relation between language and thought? Specifically, how do linguistic and conceptual representations make contact during language learning? This paper addresses these questions by investigating the acquisition of evidentiality (the linguistic encoding of information source) and its relation to children's evidential reasoning. Previous studies have hypothesized that the acquisition of evidentiality is complicated by the subtleness and abstractness of the underlying concepts; other studies have suggested that learning a language which systematically (e.g. grammatically) marks evidential categories might serve as a pacesetter for early reasoning about sources of information. We conducted experimental studies with children learning Korean (a language with evidential morphology) and English (a language without grammaticalized evidentiality) in order to test these hypotheses. Our experiments compared 3- and 4-year-old Korean children's knowledge of the semantics and discourse functions of evidential morphemes to their (non-linguistic) ability to recognize and report different types of evidential sources. They also compared Korean children's source monitoring abilities to the source monitoring abilities of English-speaking children of the same age. We found that Korean-speaking children have considerable success in producing evidential morphology but their comprehension of such morphology is very fragile. Nevertheless, young Korean speakers are able to reason successfully about sources of information in non-linguistic tasks; furthermore, their performance in these tasks is similar to that of English-speaking peers. These results support the conclusion that the acquisition of evidential expressions poses considerable problems for learners; however, these problems are not (necessarily) conceptual in nature. Our data also suggest that, contrary to relativistic expectations, children's ability to reason about sources of information proceeds along similar lines in diverse language-learning populations and is not tied to the acquisition of the linguistic markers of evidentiality in the exposure language. We discuss implications of our findings for the relationship between linguistic and conceptual representations during development.