Place two of the four plastic U-shaped pieces back-to-back, pairing each bumpy one with a smooth one. Repeat with the remaining pieces.
Wind yarn around one unit, working from one end to the other, and then back again. Continue until yarn fills the inside of the U. Repeat with other unit.
Clamp feet of units together to form a circle. If you are making the hair bobble or belt, slide an elastic band over one unit, or slip the knotted end of the belt into the center of the circle, before clamping the units together.
Snip the yarn along the circumference of the circle. Slide a piece of waxed twine between the layers of the circle, and tie in a knot, pulling tight.
Separate the units and pull them off pom-pom. Trim into a neat sphere.
Small Sharp Scissors
Who says getting bundled up isn't fun? Kids can make pom-poms using a store bought plastic maker. (They can also use two donuts cut from cardboard; stack them, then wind the whole pom-pom at once.)