In the context of increasing globalization and linguistic diversity, bilingualism has become a common characteristic of childhood. Many bilingual children are subsequently introduced to third and fourth foreign languages through formal education. While bilingualism is widely associated with cognitive and linguistic benefits, its role in facilitating or constraining additional language acquisition remains a topic of academic debate. This article examines how bilingualism influences children’s learning of third and fourth foreign languages by analyzing cognitive mechanisms, cross-linguistic interaction, and educational conditions. Drawing on research in psycholinguistics and multilingual education, the study identifies both advantages—such as heightened metalinguistic awareness and learning efficiency—and challenges, including language interference, cognitive overload, and insufficient pedagogical support. The findings suggest that bilingualism generally enhances multilingual learning outcomes when appropriate instructional strategies and supportive sociocultural environments are in place.