I cut a cardboard oval and a larger oval out of green fleece. Then I cut brown fleece in a turtle shell pattern and hot glued it to the green. I wrapped the green around the cardboard oval, leaving a section unglued for stuffing. To be totally honest, I glued the whole oval then realized I forgot to leave a hole for stuffing... it was late. So, I pulled a section off the cardboard and stuffed the shell with recycled grocery bags... a lot of them to make it nice and full. I added a scalloped "trim" piece of brown fleece around the edge to look like the edge of a shell and glued that around the edge.
You can see the scalloped trim better in this one. Now Franklin has a very predominant plastron, or lower shell to which it is commonly referred. Yes, I looked that up to sound smart... hahaha. My husband called it the chest plate. So I took some yellow fleece and just drew the approximate shape freehand on the material. Cut 2 pieces of fabric and then I cut 4 pieces of green ribbon. I would recommend using something sturdier, but ribbon is what I had on hand. Put 2 ribbons on top and one on each side. Then sew right sides together, leaving a hole for stuffing. Don't forget the hole! Trim the edges and flip right side out, like you would a pillow. I used 1" foam to stuff the chest plate so it would the shape. Stitched up the hole and stitched a few contour lines in the front.
You can see the top ribbons better in this pic. The other two were about waist level on each side. To finish it up, I glued the ribbons to the cardboard part of the shell. Then I took the second oval circle and covered all the raw edges on the cardboard to finish it. The shell just goes over the head. Franklin also wears a red hat and neckerchief. So I did a paper cut out of the sun design and taped it to a red baseball hat. I had red bandanna to tie around his neck and it was complete. I didn't go so far as to buy a green sweatsuit, like I have seen on other blogs. Just a green shirt we had and jeans. He was very happy with his costume and all the kids at school thought he was a Teenage Mutant Ninja Turtle... sigh.