The Becta publication "Using web-based resources in Primary Music" suggests a number of websites offering interactive content for use by children in music lessons. Some of the links may not always be available. However, for quick access most of the sites mentioned are listed below.
MIDI and vocal work (KS 1 & 2)
BBC Radio 3 on-line software (KS 1 & 2)
BBC Audio on demand (KS 1 & 2)
Playing with Tempo and Dynamics (KS 1)
Soundwalk in Queen Elizabeth Park (KS 2)