This is a task for either an adult or an older child due to the sharpness of the needle. You will be cursing if you poke yourself with a felting needle! These take a bit of time but the result is a nice homemade ball that is completely customizable. You can get needles and roving of your choice either locally or online. Basically all you have to do is stab your ball repeatedly; the more you stab the tighter it gets. There is a great tutorial on you tube that might help you decide what kind of needles you'd like to use. You can get as creative as you'd like and even make cute little animals. Here are a few balls I made:
N.B. If you have pets, you will want to make sure you keep these out of reach! We have dogs and although the kids' toys are generally quite safe, these are definitely not!