Freesound.org offers a huge archive of free sounds (registration for free)
opsound.org is dedicated to open source culture offering free sound & music
mp3.com free music
Bargus.org Music, sound, film, with a selection of free classic music also
archive.org huge open source page (films, music, sound, books & more)
freemusicarchive.org free music
More links on the website below (german wesbite, but listing many international sites in English)
There are HUGE archivs of free music on Youtube:
fall in love with sound design for film
Introduction to sound design (might be fun for kids 10 to 14):
sound design on TED:
Learn about film music from the best: Hans Zimmer