Resch C, Van Kruijsbergen M, Ketelaar M, et al. - Researchers conducted this systematic review to investigate which instruments were used to evaluate the participation of children with acquired brain injury (ABI) or cerebral palsy (CP) and their alignment with the concepts of attendance and/or involvement and to explore what was known about the measurement properties of these instruments in children with ABI or CP. Thirty-seven instruments have been used to evaluate participation in children with ABI or CP. Of those, 12 measured attendance and/or participation. In 14 studies with children with ABI or CP, the reliability, validity, and responsiveness of eight of these instruments have been analyzed. For most of the measures, adequate measurement properties were recorded, but no instrument on all the related properties had been assessed. Instruments for measuring children's engagement with ABI or CP should be carefully selected, as many available measures do not align with attendance and/or involvement. Evidence for measurement properties is limited, caused mainly by low methodological study quality. The recommended methodological guidelines should be followed for future studies.