We used to make toys for the neighbours cat.

Cut two same size circles out of cardboard and place them together (and then cut a large hole in the middle). Take a ball of wool and wrap it around continuously until you've filled the hole. (Should take a while.)

Then using a pair of scissors cut the wool around the edge of the circles. Tie it in the middle (between the two pieces of card and really tight) and it gives you a small ball that they can play with.