I started with some roving. You have to really fluff it out to get a lot of fibers available to grab each other during the shock of felting. It is important to pull the roving apart rather than cutting it. Cutting it will cause cracks later.
I rolled the roving loosely into a ball, then filled a small, reusable leftover container with about half a drop of dish soap and a couple of teaspoons of water. After experimenting a bit, you'll see how much water works.
However, ALL of my balls got some sort of crack. Even when I didn't cut the roving. I found that if you stuff a small, thin layer of new roving in the crack, then wrap it around the ball using a little water as "glue," you can heal the crack pretty well.
It worked! These balls were really cute and Starboy loves to play with them. Mine turned out light and fluffy. I have seen others that are more smooth and dense. I wonder if this is because the roving initially was wound much more tightly? I will have to experiment.