These are a teachers-screened set of YouTube videos explaining and illustrating the science of sound for students in grades 3-12. Learn how the ear works, frequencies and propagation of sound waves.  All videos and lessons on this site have been reviewed by K-12 teachers and are safe for kids.

Explore sound in these simulators.  They include a tone generator and a variety of wave generators.  You control for pitch and sound.

From site:  The Soundry is an exciting, interactive, and educational web site about sound. Covering everything from the most basic concepts of what sound actually is to the specifics of how humans perceive it, The Soundry aims to promote enthusiasm and knowledge of sound. We hope you have fun exploring our site and come away with new understanding and insights about sound.

LearningReviews note:  This website was created by Virginia high school students.  It provides detailed information on how we perceive sound in the ear, the physics of sound, applications of sound, and an interactive sound lab where you can play with sounds and views their wave patterns.