With the emergence of new technologies, there has been an explosion of basic and clinical research on the affective and cognitive neuroscience of face processing and emotion perception. Adult emotional face stimuli are commonly used in these studies. For developmental research, there is a need for a validated set of child emotional faces. This paper describes the development of the National Institute of Mental Health Child Emotional Faces Picture Set (NIMH-ChEFS), a relatively large stimulus set with high quality, color images of the emotional faces of children. The set includes 482 photographs of fearful, angry, happy, sad and neutral child faces with two gaze conditions: direct and averted gaze. In this paper we describe the development of the NIMH-ChEFS and data on the set's validity based on ratings by 20 healthy adult raters. Agreement between the a priori emotion designation and the raters' labels was high and comparable with values reported for commonly used adult picture sets. Intensity, representativeness, and composite "goodness" ratings are also presented to guide researchers in their choice of specific stimuli for their studies. These data should give researchers confidence in the NIMH-ChEFS's validity for use in affective and social neuroscience research.