The current study examined monolingual English-speaking toddlers' (N=50) ability to learn word-referent links from native speakers of Dutch versus English, and second, whether children generalized or sequestered their extensions when terms were tested by a subsequent speaker of English. Overall, children performed better in the English than in the Dutch condition; however, children with high native vocabularies successfully selected the target object for terms trained in fluent Dutch. Furthermore, children with higher vocabularies did not indicate their comprehension of Dutch terms when subsequently tested by an English speaker whereas children with low vocabulary scores responded at chance levels to both the original Dutch speaker and the second English speaker. These findings demonstrate that monolingual toddlers with proficiency in their native language are capable of learning words outside of their conventional system and may be sensitive to the boundaries that exist between language systems.