Have an easter egg hunt or a scavenger hunt around the farm. I've had "haystack hunts" before, hubby piles up a huge pile of chaff with the loader and we hide eggs or prizes in the pile then the kids race to find them all. Sometimes each kid is assigned a color and is only allowed to pick up that color egg. Play pin the tail on the pony (paint a picture of a pony and make ribbon tails to pin on them). Have an egg and spoon race with plastic easter eggs on horseback, or in hand if they don't ride. Play a game of horseshoes with real horse shoes or set up a craft table and let them paint lucky horse shoes. Set up hula hoops and have them play ring toss with green carrots (ponies will enjoy eating the carrots). Or play corn hole with carrots or plastic easter eggs. Have the kids run a grain sack race or 3 legged race, tying the legs with hay twine. Have the kids run a duckling waddle race (they bend over and grasp their ankles and waddle to the finish line). Print out coloring pages and have them color their favorite pony a picture or get them to collaborate together to write a story about a day on the farm. You could hard boil eggs and have them color easter eggs. My favorite was the bunny tail game, divide them into two teams, each with an empty bowl and one full of cotton balls. The ref puts a dab of Vaseline on their noses and they have 30 seconds to get as many cotton balls into the empty bowl with their nose as they can. Have fun.