Most of a turtle costume is taken care of by buying a green sweatsuit. That leaves you with the task of creating the carapace. Choose from several different methods to make a turtle shell that's easy for your child and looks amazing when worn.
Papier Mache Shell
Find a large basin that's ovular and the right size for the wearer of the costume. Coat the bottom of it in cooking oil to prevent the papier mache from sticking to it.
Mix 1 cup flour with 1 1/3 cup water and 1 tsp. salt to make a paste.
Rip newspaper into 1-inch long strips. One at a time, coat the paper with paste and lay it to cover the bottom of the basin. Using a crisscross pattern makes the shell stronger.
Smooth out any excess glue, using a large paintbrush.
Allow it to dry at least overnight. Carefully take the papier mache shell off the basin.
Coat the shell with white paint and let it dry. Paint both sides of the shell green. When the green paint dries, add decorations, such as spots, with another shade of green to look like a turtle shell.
Glue the side seams of a yellow shirt or vest to the edge of the open side of the shell to make the front of the shell.
Cut two large ovals out of light green or yellow felt. The ovals should be as long as the torso of the costume wearer and approximately eight inches wider.
Cut out two more ovals of the same size from a dark green felt.
Glue the ovals of the same color together. This makes a stronger shell than one layer of felt would. Hold the felt oval up to the costume wearer and mark where the arms and head will go. Sew together the ovals, leaving the bottom open for the legs and enough room for the head and arms.
Turn the costume inside-out to hide your stitches. Paint the back of the shell with acrylic or fabric paint to look like a turtle shell.
Stuff a backpack with newspaper or clothing. The backpack will go under the shell to give it a more filled-out appearance.
Paint an old bicycle helmet with light green acrylic paint. Let the paint dry.
Paint dark green spots to resemble a turtle shell.
Put the helmet on the child’s back, using the chinstrap to help it stay in place.
Watch the child at all times and remove the helmet while traveling, or while the child is sitting.