How old is your child? Mine was very interested in classical music from an early age and I used the resources from Classical Kids -
http://www.classicalkidsnfp.org/shop/There are also movies in DVDs available that matches the Classical Kids CDs which are very good.
Beyond that, we read a lot of books about composers and always had classical music playing in the background in the house and the car. Our local classical music station also talks about composers and little trivia about them and their times before playing each piece which tremendously helped my child learn about music history.
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