This chapter discusses the ways in which research has been undertaken with children in applied linguistics and ELT. First of all, the traditional paradigm is introduced and it is argued that most research to date has involved children as passive objects of adult interest. Even where children have been studied as unique subjects with their own characteristics and trajectories, all aspects of these studies have also been completely controlled by adults. An alternative paradigm which considers children as competent social agents is proposed, and, accordingly, the chapter recommends that it is possible to work with children as active subjects and co-researchers, and even to enable them to become researchers themselves. Children can influence and have useful input into research that concerns them and their learning. The consequences of this shift from passive to active research participants brings numerous benefits but also significant challenges. This chapter gives an overview of these benefits and challenges and suggests some practical recommendations for classroom research with children.