Whenever I teach or fill in for an elementary level C.C.D. class (to tell you the truth, middle-schoolers love this too!), I try to dig up a string trick and work a bit of religion into it. It's always a hit ... the kids love being active and the lesson learned really sticks. This string trick is known much better as the "Cup and Saucer," however, it doesn't take much imagination to see that it also resembles a manger.
First of All ... Teach the class a bit about why Jesus used a manger as His bed when He was first born. Read the passage out of the Bible (Luke 2:1-7) or tell the story using a picture Bible. If possible, show them a picture of the Baby Jesus sleeping in the manger. Try to get the kids involved by asking them questions like ... How comfortable is your bed? Do you think you'd like to sleep on straw? In a stable? Why do you think God had His only son begin his life under such difficult circumstances?
Secondly ... Give each student a piece of string (about 50 inches long, ends tied, creating a loop) and then show the video below. Tell them they must try "The Manger" string trick 5 times before giving up. For the really fast learners, have them do "The Manger" 10 times with their eyes opened and then 10 more times with their eyes closed. Then, have them help out some of the others in the class who need some extra help.
(a.k.a. Cup and Saucer)