I think shop bought costumes are rubbish, they take away most of the fun of the nativity play. Most of the cuteness factor is in the shepherds with their tea towel headgear, kiings with cardboard crowns with foil on them, and angels in sheets and tinsel!
My son was once a sheep and we used ironing board clips to put my small sheepskin rug on his back, and made a sheep mask stapled to a pull on hat. He was hilariously cute.
