Here is an idea of the Opera unit study I have put together for my kids. We do music together despite the difference in age (K and 3rd grade).
Bantam of the Opera by Mary Jane Auch-a cute picture book about a rooster with a passion for fine music.
The Dog who Sang at the Opera by Jim West and Marshall Izen
Phantom of the Opera Musical by Andrew Lloyd Webber
coloring page of Andrew Lloyd Webber
Die Walkure (The Valkyrie) by Eichard Wagner
Valkyrie coloring pages
Hansel and Gretel by Englebert Humperdinck
Read the fairy tale by the Brothers Grimm
or listen to the Golden Book version on you tube: http://www.youtube.com/watch?v=UoWfkuiTMs8
Metropolitan Opera Educator Guide
Little Red Riding Hood by Seymour Barab
Watch the Golden Book version on you tube: http://www.youtube.com/watch?v=5CkCpx3CE2Q
Metropolitan Opera videos on demand
You can "rent" a video for 30 days, or do a free 7 day trial. I think this would be an amazing tool to watch different versions of a production, and compare sets, costumes, and performances.
There are quite a few opera for kids CDs out there as well. Try your local library.
Design your own opera online game: http://www.classicalkusc.org/kids/opera/index.asp
This is an extremely well done interactive game which lets the students try out various roles from the production of an opera, like lighting, choreography, costume, and props.