The aim of this article is to introduce the use of the child diary as a method in daily diary research. By describing the research process and detailing its structure, a child diary, a structured booklet in which children's parents and day-care personnel (N = 54 children) reported their observations, was evaluated. The participants reported the use of the diary to be an interesting but time-consuming experience. The main ethical challenges were related to power positions, confidentiality, consequences and motivation. With respect to adults' observations of children's emotions, the results indicated that the child diary is valuable in providing information about individual differences and daily dynamics and that the diary reveals some of the conventions in child-related everyday interactions in home and in day-care environments. In addition to its use as a research method for capturing situation-specific information in the family and day-care contexts, the child diary also serves as a tool in collaboration between parents and day-care personnel aimed at enhancing children's well-being. (Contains 2 figures and 2 tables.)