In this article, we examine how young climate activists make use of the United Nations (UN) constituency system to give voice to children and youth in global climate governance. Our study is based on a mapping of accredited youth nongovernmental organizations (YOUNGO) as well as fieldwork at two UN Climate Change Conferences, where we conducted interviews, observed events, and analyzed plenary interventions. Informed by constructivist accounts of political representation, the article pays attention to the performative relationship between institutionalized means of youth representation and “the represented.” When analyzing our material, we asked who speaks for youth, how youth are spoken of, and how institutions shape representative speech. Our study identifies three subject positions that offer competing interpretations of who youth are as a political community and what they want. Rather than taking youth’s demands and interests as a starting point for representative politics, the article illustrates how the UN constituency system actively constructs youth and effectively molds young climate activists into professional insiders.