As you listen you might want to try this idea from my mom's blog: Coloring to Classical Music.
If you are interested in studying a little more about Vivaldi you can check out the Harmony Fine Arts Free Dowload (Vivaldi is on page 8 of the PDF). It has links to biographical information and online listening.
If you want to purchase a Vivaldi CD from Amazon, here are some to get you started: (We own the first one and highly recommend it.)
And if you haven't seen my summer themed art, handicraft and nature study kit, check it out here!