Instead of boring said child with your own answer, why not sit the little cherub down in front of this wonderful animation. It manages to take in around ten thousand years of musical history in a little over three minutes and should answer the first question rather well - although it may provoke even more.
This short animation was part of the Science Club series on the UK TV channel BBC2 hosted by Dara O Briain. It was created by Asa Lucander.
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