This thesis discusses the multiple ways of knowing and relating to the world developed by indigenous Matses children in Peruvian Amazonia. Its primary focus is a detailed exploration of children's lived experiences and understandings, whereby I try to bring out how young Matses develop a sense of their being-in-the-world through everyday interactions, movements and the imagination. I focus specifically on how children participate in and actively contribute to ongoing processes of transformation in Matses society. These include, amongst others, Matses recent shift from living itinerantly in the forest to sedentary life in riverine dwellings; the growing relevance of money, manufactured goods and the national market economy; and increasing exchanges with nonindigenous peoples and travels to their settlements.Accordingly, this research explores how children living under radical conditions of change develop new possibilities of being amidst the opportunities and constraints of the present. I argue that far from being simply caught up in wider social processes, the children become active agents of transformation within Matses society and play a profound role in directing the course of social life towards certain directions and away from others. This is not, I argue, because children exert political, outspoken control over the wider community, for instance by making decisions for the adults or by publicly expressing their opinion to the adults. I argue, instead, that simply by developing original ways of knowing and making sense of the world, the children actively move away from the lifestyle and knowledge of old generations and set up tangible conditions for alternative possibilities of life in the future.The thesis therefore attempts to put forward a view of social transformation in which children are recognised as dynamic agents of change, and in which changes are addressed not just in terms of an intergenerational comparison, that is, in considering how life in the present is different from the past or in how children's knowledge and ways of being differ from those of their elders. Rather, I also consider the future as constitutive of change and attempt to propose an analysis of children's future horizons in ethnographic terms; which means that I recognise children's desires and aspirations as triggers of transformation, insofar as by working towards their wishes and expectations the children set up the tangible possibilities for different future livelihoods and in so doing set change in motion.