I covered a short mailing tube with decorative paper and used a small stuffed animal for the puppy. If you don't have a puppy you could use any little creature that's the right size. If you don't have a mailing tube, you could use a plastic container that's cylindrical and cut out the bottom. A tall frosting container would work.
For the Senior Primary I challenge them a bit more. The more they see of the puppy, the louder they have to sing. If he goes inside the tube they stop singing, but the piano keeps playing. They have to keep track of the lyrics in their head and then start singing again when the puppy pops up. I let the kids take turns making the puppy pop up and they have a blast!