Perceived exertion during exercise: is their measurement valid in children? The perceived exertion (PE) corresponds to the subjective sensation caused, in part, by the metabolic changes during exercise. This variable has been widely used during exercise tests and during training processes and physical rehabilitation in healthy and chronically diseased children. Additionally, it has been established that the assessment of PE properties (validity and reliability) is strongly determined by the type of scale, the applied paradigm and the cognitive development. Evidence is overwhelming in establishing the validity of this measurement in children aging from 4 years old, by using adapted scales. At 8 years-old the application of estimate-production paradigm is suggested and from 13 to 15 years-old the Borg scale 6-20 would be used. In Chile EPInfant scale has been developed for measuring child perceived exertion. This scale has shown an acceptable performance in incremental exercise test in healthy children aged 8 to 15 years old, justifying its use. We review the assessment of PE properties in children , considering key aspects in the design of scales and cognitive development of children. Additionally, the evidence regarding the validity of the Chilean scale EPInfant in children is presented. Finally the research currently under development and its projections on this issue are discussed.