Despite wide usage of the Numerical Rating Scale (NRS) for self-report of pain intensity in clinical practice with children and adolescents, validation data are lacking. We present here three datasets from studies in which the NRS was used together with another self-report scale. Study A compared post-operative pain ratings on the NRS with scores on the Faces Pain Scale-Revised (FPS-R) in 69 children age 7–17 years who had undergone a variety of surgical procedures. Study B compared post-operative pain ratings on the NRS with scores on the Visual Analogue Scale (VAS) in 29 children age 9–17 years who had undergone pectus excavatum repair. Study C compared ratings of remembered immunization pain in 236 children who comprised an NRS group and a sex- and age-matched VAS group. Correlations of the NRS with the FPS-R and VAS were r = 0.87 and 0.89 in Studies A and B, respectively. In Study C, the distributions of scores on the NRS and VAS were very similar except that scores closest to the no pain anchor were more likely to be selected on the VAS than the NRS. The NRS can be considered functionally equivalent to the VAS and FPS-R except for very mild pain (<1/10). We conclude that use of the NRS is tentatively supported for clinical practice with children of 8 years and older, and we recommend further research on the lower age limit and on standardized age-appropriate anchors and instructions for this scale.