We monitored the progress of 40 children when they first started to acquire a second language (L2) implicitly through immersion. Employing a longitudinal design, we tested them before they had any notions of an L2 (Time 0) and after 1 school year of L2 exposure (Time 1) to determine whether cognitive abilities can predict the success of L2 learning. Task administration included measures of intelligence, cognitive control, and language skills. Initial scores on measures of inhibitory control seemed predictive of L2 Dutch vocabulary acquisition. At the same time, progress on IQ, inhibitory control, attentional shifting, and working memory were also identified as contributing factors, suggesting a more intricate relationship between cognitive abilities and L2 learning than previously assumed. Furthermore, L1 development was mainly predicted by performance on inhibitory control and working memory. (PsycINFO Database Record (c) 2018 APA, all rights reserved).