Well it depends on how much money you have to blow. You could rent a pony with a handler. Some stables offer party packages with trail rides. Or, you could buy two or three stick horses and have stick horse races. Play pin the tail on the donkey. I have seen those with a horse instead of a donkey. Buy a horse pinata. Get a cake with a horse on it. You could also do an age appropriate scavenger hunt around your yard where once again they use the stick horses to gather the items. Make a saddlebag for them to put there items in. Watch a kid friendly movie about a horse like Flicka. Or you could go with the ktten theme and decorate cupcakes to look like kitten faces. Of course, a cat pinata. Do a craft with styro foam balls, pipe cleaners, etc. and have them make a kitten. You would need to make one first to give them the idea. Hide some little toy mice around the room or yard and have them pretend like they are kittens hunting for the mice. Whoever finds the most mice will get a little prize of some sort. Tie a balloon to a cats tail and when the cat runs have them chase it. LOL J/K Kids that age are not very hard to please. Keep them involved so you don't find yourself running in a hundred directions.

You could get a pinata (spelling?) or pin the tail on the pony or kitty or have a hunt for the kitty place clues around the yard for them to find. or a coloring contest.