This paper examines children’s interaction during authentic lessons involving tasks in L2 classrooms, comparing the effects of teacher guidance for 5–7 year olds (n = 22) and 11–12 year olds (n = 20). Three experimental conditions representing a continuum of teacher guidance were examined: task instructions alone, task instructions with examples, and task instructions followed by on-task guidance and feedback. In all conditions, regardless of age, children interacted in ways deemed facilitative of language learning, although older children seemed to benefit most from on-task guidance. These findings are discussed in terms of the potential benefits of tasks for L2 production and interaction in children’s ESL classrooms, as well as the under-researched but important role of the teacher’s input and guidance.