The project is situated in the field of phonology and aims to provide an in-depth analysis of how childrenacquire the sound system of a second language (L2). While previous research has shown that an early L2starting age is beneficial for the ultimate attainment of L2 phonology acquired in naturalistic settings, there is a dearth of studies on the developmental paths taken by children with limited, instructed exposure to the target language. While the number of schools in non-English speaking countries offering English initiation classes in primary schools is growing, little is known about the effect of this early L2 exposure on the child’s developing L1 and L2 phonologies. Does the children’s L2 phonological system develop with only limited exposure to the target language, and if so, how and when? What is the extent of cross-linguistic influence between the L1 and the L2 for children of different ages? The proposed project aims to answer these questions by means of a longitudinal study with native speakers of Dutch, aged 4;0–5;0 and 10;0-11;0, learning English in a school setting. Both production and perception data will be gathered at regular intervals in the school year to make it possible to map the development of each child’s L2 phonological system.