The present study aimed at investigating whether L2 learning affects phonological short-term and working memory and first language (L1) development. The performance of a group of 31 4- to-5-year-old sequential bilinguals attending an International School on tasks assessing phonological short-term and working memory and linguistic performance in L1 was compared to that of a group of 31 age-matched monolinguals. The bilingual group outperformed monolinguals on two simple and one complex span task assessing phonological short-term and working memory, respectively. They performed as monolinguals on measures assessing articulatory skills, phonological abilities, naming and grammatical processing in L1. However, bilingual participants performed worse than monolinguals on a test of lexical comprehension. These results are discussed in light of current models of cognitive development.