Trace a broad five-pointed star about 15 cm across onto cardboard. An adult cuts it out and trims any rough corners. Wide points are easier to wrap than narrow ones.
Tape the end of a short arm-length piece of yarn to the back. Wind across the center a few times, keeping the yarn snug enough to stay put without bending the cardboard.
Wrap diagonally from point to point, rotating the star as you work. Cover the center first, then change direction to cover the broad points. Tape a new short length to the back when needed; a few visible cardboard edges are fine.
Tuck the final yarn end under a back strand and tape it flat. Set the star on a shelf or tape it to a wrapped gift; press gently to keep the cardboard flat.
A little help: Adults cut the cardboard. Use short yarn lengths, put away loose strands afterward, and keep the finished decoration and yarn away from young children and pets.