In this article, I focus on a group of people whose voices in archival materials are especially hard, or very unusual, to find. This group comprises intellectually "abnormal" children. Using the example of German-speaking Switzerland and focusing on the late 19th and early 20th centuries, I will show the types of materials produced on the welfare and education efforts concerning intellectually "abnormal" children, and will analyse those that were preserved and are accessible today. Adopting the closer focus of this special issue, I will then indicate whose voices can be found in the source materials, and whose cannot. This research interest is linked to the concept of agency, which for some time has received increasing attention but also criticism in childhood studies and in childhood history. According to the agency concept, children -- akin to adults -- are considered competent social agents who have their own voice. I will juxtapose this premise with historical sources on intellectually "abnormal" children and put forward the argument that focussing on agency is not very productive when it comes to writing the history of these children.