Over the last 30 years, remarkable efforts have been made to understand and support children and young people's participation rights outlined in the UN Convention on the Rights of the Child (UNCRC). Despite these efforts, challenges remain consistently the same, such as tokenism, lack of sustainability, and accountability. This article reviews the progress and challenges for children and young people's participation. It then considers the potential of activism as a relatively novel concept for the children's rights field. Drawing on activism literature more generally, and considering examples of child activism, the article explores the potential of identity politics and social movements to challenge adult power, growing on-line activism and tensions between best interests, protection and participation. The article concludes that activism recognises children as political actors and problem solvers. The article develops the idea of an 'ecology of participation', which values respectful intergenerational relationships that develop 'critical social capital' for child activism and multiple participation forms -ranging from the more conventional, to protest, to transformation. This more extended conceptualisation of children and young people's participation builds on all the participation rights within the UNCRC, recognising them as minimum standards rather than final destinations, to create more expansive understandings and practices.