When the European Union Youth Orchestra (EUYO) last appeared on this stage, The New York Times called the performance “nearly indistinguishable from what any fine orchestra out to make an impression at Carnegie Hall might present.” The most notable difference? The “infectious joy evident onstage.” As part of Carnegie Hall’s World Orchestra Week (WOW!), celebrating outstanding youth ensembles from around the world, conductor Iván Fischer leads the orchestra and acclaimed pianist Isata Kanneh-Mason in a program that includes Mahler’s First Symphony; Dohnányi’s Variations on a Nursery Tune, Op. 25; and a brisk opening piece by Anna Clyne.