This article presents findings from a qualitative content analysis of 531 Little Golden Books that contain early childhood marginalia--any physical alteration of a book, resulting from an exercise of reader agency by a child from birth through eight years old. The primary goals of the present study were to expand the reach of this methodology by investigating the characteristics of early childhood marginalia and exploring the use of the methodology to study children's earliest un/mediated reading experiences. The findings from this study indicate that the qualities of early childhood picturebook marginalia make it a useful methodology for literacy researchers and educators interested in exploring aspects of young readers' (a) literacy learning, (b) reader intent/purpose, (c) text-specific interest and response, and (d) reader identity.