Easy sew (or glue!) turtle shell tutorial. Plus instructions for other animal costumes. Handmade, green felt, upcycle cardboard box, homemade, good for toddlers and babies. First cut a toddler backpack size oval out of your cereal box (mine is about 13" tall and 9.5" wide). Lay this over your base green felt. You will need one large piece of felt OR sew little pieces together like I did :) Work with what you have!