While vocabulary knowledge is considered a foundational element for young learners of a second or foreign language (L2/FL), pedagogically useful information on this topic is not easily accessible for practitioners. This is in part due to the fact that the relevant information is scattered across multiple fields, including first-language acquisition, child development, and education. The aim of this paper is to synthesize recent knowledge from the related fields and to provide theoretically sound and evidence-based information that is useful for teaching vocabulary to young learners of L2/FL. It identifies four major recommendations for vocabulary instruction: (a) ensure frequent and repeated exposure to the target words (as well as nontarget words); (b) provide explicit word definitions and meanings in context; (c) create opportunities for discussions and interactions around the words in question; and (d) use multimodal approaches to teach vocabulary. The paper also suggests future research directions, with the goal of finding effective approaches that teachers can use to improve their vocabulary instruction while meeting the specific needs of their young L2/FL students.