Here's a really fun site with games designed for different age groups. http://www.kidsdomain.com/games/music.html
Learn about American music and more at this site. http://www.kids.gov/k_music.htm
Listen to free music for kids at this site. http://www.freekidsmusic.com/
Learn about composers or draw a musical picture at this site. http://www.kidsites.com/sites-edu/music.htm