1.  The Dallas Symphony Orchestra has multiple links on their DSOkids, website, instruments, musicians and composers.

 https://www.mydso.com/dso-kids/

2.  A YouTube site with basic music theory

     The Music Show Episode #1:  There are multiple episodes

      https://www.youtube.com/watch?v=0kaX2l413p8 

3.  Little Amadeus - up to 14 episodes about the composer Wolfgang Amadeus Mozart

    https://www.youtube.com/watch?v=GXM9sUMzYhY&t=24s

4.  Music Instruments and musicians

     https://www.youtube.com/watch?v=0A6XwFWD-z0