If you're teaching early balls skills, take a look at the Protex 9. It's colourful, child-friendly, in moulded foam and with a good, regular bounce.
9cm diameter (for comparison, a regular tennis ball is around 7cm
A great choice for playgroups and nurseries, the Protex 9 is bright, soft, safe, and squeezable. It's also a very good ball for early multi-sport activities, as well as early 'tots' Mini Tennis.