Try these sites for great online music learning options:
Classics for Kids - Fun interactive music education games for kids
Joytunes - Bringing music learning into every single household around the world, whether it’s piano, guitar, sax, singing, or any other instrument
MusicTheory.net - Lessons, tools, exercises and more
Yousician - Yousician offers thousands of songs, exercises, and teacher-crafted lessons all in one app
Noteflight - Create, teach, share, sell and purchase music
Guitar Pro - Access to thousands of tabs
Jazz Tutorial - Learn Jazz Piano online with step by step video tutorials
Musescore - Create, play and print sheet music