The current study examined to what extent information in long-term memory concerning the distribution of phoneme clusters in a language, so-called long-term phonotactic knowledge, increased the capacity of verbal short-term memory in young language learners and, through increased verbal short-term memory capacity, supported these children’s first and second language vocabulary acquisition. Participants were 67 monolingual Dutch and 60 bilingual Turkish–Dutch 4-year-olds. The superior recall of nonwords with high phonotactic probability compared with nonwords with low phonotactic probability indicated that phonotactic knowledge was supportive for verbal short-term recall in both languages. The extent of this support depended on prior experiences with the language: The Turkish–Dutch children showed a greater phonotactic probability effect in their native language Turkish compared with their Dutch peers, and the monolingual Dutch children outperformed the bilingual Turkish–Dutch children in their native language Dutch. Regression analyses showed that phonotactic knowledge, indicated by the difference in recall of nonwords with high versus low phonotactic probability, was an important predictor of vocabulary in both languages.