Music:

 

Games/Worksheets (The majority of these are free!)

Piano Learning Center (Resources covering a wide variety of aspects of the piano, written by piano technicians!)

Rhythm worksheets from Composecreate.com

A free piano coloring sheet by Susan Hong

Theory worksheets from MakingMusicFun.net

Note-naming worksheets from The Perfect Start for Piano

Alphabet Trail Game

Some fun music resources from Susan Paradis

 

Other Resources

Musescore (a free software for composing and writing out music)

Chrome Music Lab (an interactive online music lab)

A Piano Parent Podcast (for all your questions as a piano parent)