Using the metaphors "body" and "voice" and drawing on critical contributions on biopolitics, this article interrogates children's participation rights in a knowledge culture of 'evidencing'. With child welfare and protection practice as an empirical example, I analyse written assessment reports from a Swedish child welfare agency, all exemplifying how social workers evidence needs for protection and reasons for removing children from the home. I discuss how 'evidencing' equals a knowledge culture of "seeing-believing" and "predicting-believing" and the search for visibly damaged bodies and underdeveloped minds. I furthermore problematise how such conceptualisation of evidencing foregrounds children's 'speaking' bodies while silencing their voices. By showing these manifestations of evidencing, this critical contribution discusses some wider epistemic concerns for fields influenced by the knowledge cultures of 'the evidence-based'.