Cut out a single turtle shell from the egg carton (just one hump). Choose one shade of green and paint the outside of the shell.
While the shell is drying, cut two rectangles (1/2" x 3 1/2") out of construction paper or craft foam to make legs. Cut two little triangles into both ends of each rectangle to add feet to the legs.
Cut one rectangle (1" x 4") out of construction paper or craft foam. Trim one end to make a pointy tail. Round off the other end to make a head. Draw eyes on the turtle's head or add google eyes.
When the shell is dry, use the other shade of green paint to make designs on your turtle's shell. Be creative!
When the shell is completely dry, glue the legs, tail, and head to the bottom rim of the egg carton shell. The body parts should poke out from under the egg carton like a turtle would from under its shell.