The San Francisco Orchestra maintains this kid-friendly music education site. They state that, “We love music and are committed to music education, within our community and beyond. This website, in conjunction with our live performances, provides a great way for people of all ages to hear, learn, and have fun with music.”
Your students will enjoy learning about the parts of an orchestra and creating their own music.
"Smarthistory.org is a free and open, not-for-profit, art history textbook. We
use multimedia to deliver unscripted conversations between art historians about
the history of art. We are seeking contributors—especially for canonical
non-Western material and other survey topics not yet covered."