What You Need: Diaper box (or box about twice as tall as your toy cars, and comfortably wider), two paper towel tubes, foam or felt sheets, wooden spoon, dowel rod, straws, tin foil, X-acto knife, scissors, paper and markers.
How to Do It: Cut off the top of the box, cut fold-down car-size doors on either end, and cut windows on each side. Cut felt or foam sheets into fringed strips and glue around one paper towel tube to look like a large car-wash brush. Wrap a wooden spoon in aluminum foil and put through the fringed tube. Cut notches into the top of the box near the car-wash entrance so the wooden spoon can slip into the notches and allow you to spin the brush. Cut the other paper towel tube in half lengthwise, cover with foam or felt fringe, and glue to the back corners of the car wash. Glue a long fringed sheet of felt or foam to a dowel rod to make a washing curtain. Cut notches into the top of the box to suspend the dowel rod and its curtain in the middle of the car wash. Glue another fringed curtain of felt or foam right inside the entrance opening. Decorate the outside of the box with aluminum foil and paper signs, and invite Barbie to bring her convertible for a deluxe wax and shine.