Chrome Music Lab: https://musiclab.chromeexperiments.com/

NY Philharmonic Kidszone: https://www.nyphilkids.org/

PBS Kids Music: https://pbskids.org/games/music/

Classics for Kids: https://www.classicsforkids.com/

San Francisco Symphony Kids: http://www.sfskids.org/

Music Theory Note Trainer: https://www.musictheory.net/exercises/note

Young Person's Guide to the Orchestra:  https://listeningadventures.carnegiehall.org/