Physical function can be assessed through physical examination with the use of performance-based measures and patient-reported outcome measures (PROMs). Each form of assessment provides a unique contribution to the understanding of the impact of rheumatologic conditions on the patient. PROMs of physical function (PF) are an important component of the assessment of children with arthritis and have been included in the recommended core set of measures for childhood arthritis and musculoskeletal conditions. These measures provide the child’s or parent’s perspective of function within the context of daily living. Measures of PF include both generic measures, which are designed for use across a spectrum of diseases and within healthy individuals, and disease-specific measures, which are developed intentionally for children with a rheumatologic or musculoskeletal condition. Most PF PROMs include items that relate to daily functional activities, but not all include aspects of daily living, play, and recreation, which are activities essential to the physical, social, and emotional development of children.