I didn’t know much about composers when we started either, Robin. (And I had taken piano for several years.) It really helped to change my thinking from “covering the composers” to “getting to know” one composer at a time. So we found a CD with the music of one composer. (I think we started with Beethoven, because he was one I knew from piano lessons.) It wasn’t all of his music, but it was enough to give us a feel for his style. We listened to that CD in the van when running errands or sometimes during lunch or sometimes I played it while I was fixing supper and the kids were within earshot. I just told them, “Let’s listen to some Beethoven,” and started the CD. After about six weeks, we switched to a different composer and repeated the process. Nothing elaborate or formal. Just getting to know each one’s music and style.
If I could find a good living biography about the composer we were listening to, I would read it aloud one or two days a week. But usually we just listened to his music. With this method, we got to know about six different composers each year. Multiply that times five or six years of doing this simple technique, and you’ll get to know thirty or thirty-five different composers.
Oh, and even if you can’t find a good living biography, be sure to put each composer in your Book of Centuries. That’s a fascinating exercise to see what was happening during each one’s lifetime. You can find out their life years by checking Wikipedia or some other online reference.
If you want a list to get you started, here is a list of many of the composers that we listened to over the years (and still do). Many of them have become “old friends” now. 
