I recently had to do the same thing. I did a search for rocking horse patterns and just horse clip art and copied the eyes from one of those. They turned out even better than I expected. I can email you the ones I saved to pick from.

For large eyes I have used the bottle tops to a two liter, or a gatorade bottle, (any juice) and cut a sponge to size. Then I "sponge" the eyes on lightly, and after it is dry I fill in the white with a brush, dabbing. For the black, I use the ends of a paintbrush dipped in black of course!:) But I have also used a sized cut sponge as well, glued or taped on the end of a paintbrush, dab, and fill in!! Great luck!! Hope I helped, enjoy!!!!