This study examined how cross-age peers (ages 5-6 and 9-10) used and responded to Spanish (L1) as they read and talked about informational texts together written in English (L2). Grounded in sociocultural discourse analysis, we analyzed video recordings and transcripts from 10 sessions of peer reading in two elementary schools. We coded student talk to understand L1 language functions in this context and found that students employed L1 for task management, clarifying language, negotiating content, building relationships, and checking for understanding (in this order of frequency). We discuss quantitative patterns and qualitatively analyze student interactions that show affordances and challenges using L1 in literacy activities. This study contributes to scholarship by shedding light on a previously under-examined context (cross-age peers reading L2 texts) and by offering a coding scheme for analyzing interlocutors' responses to L1 use in terms of engagement in learning activities and subsequent language use. Findings have implications for educators to consider how L1 can be used in peer discussions, reading materials, and teacher language as pedagogical tools, which should respond to learners with varying L1/L2 literacy backgrounds.