In middle schools and high schools across the country, students analyze primary sources, engaging with and asking critical questions about historical documents. But the students who generated these observations, reflections, and questions were kindergartners--five- and six-year olds, working with Library of Congress staff to help refine strategies for teaching with primary sources in the early grades. The power of primary sources has long stood at the core of the educational mission of the Library of Congress. As the world's largest library, the Library makes more than 50 million of its unique historical artifacts available online at its website, loc.gov, free for all to use. When used effectively, these primary sources can engage students in complex topics and support them as they build their critical thinking skills and create new content knowledge. This article describes a preliminary investigation that provided the authors with a more focused opportunity to observe young learners working with primary sources.