Research has shown that tasks provide second language (L2) learners with many opportunities to learn the L2. Task repetition has been claimed to benefit L2 learning since familiarity with procedure and/or content gives learners the chance to focus on more specific aspects of language. Most research on task repetition has focused on adult populations, but child learners are an under-researched group. The same goes for first language (L1) use during L2 interaction, which has been mainly studied among adult L2 learners whereas little is known about L1 use among child L2 learners interacting while they complete communicative tasks. This study explores to what extent and for which purposes children in an English as a foreign language (EFL) setting use their shared L1 (Spanish). Furthermore it also considers how task repetition (exact vs. procedural task repetition) influences their L1 use. Forty-two EFL learners worked in pairs while they completed a spot-the-difference task twice. Our findings showed a significant decrease in L1 use when learners repeated the task in the two conditions but a minor effect of task repetition on the functions the L1 served.