A play day or fun day is a great way to break up the winter doldrums or fill a gap in the show season. The first thing you'll want to do after you've invited everyone is to make sure that all parents know what is going on. They should sign waivers. It sounds nit-picky, but things can get ugly between even the best of friends if someone gets injured. Everyone needs to have properly fitting helmets, footwear or safety stirrups, and safe riding equipment.
Games to Play
If all of your friends are riders, and it's okay with parents, traditional gymkhana games can be played. These include speed games like barrel races, pole bending, keyhole race, apple bobbing, or skill games like egg and spoon, and ride-a-dollar classes. Always keep in mind the skill of the riders and the space you have to play in.
If you only have a few horses and lots of riders you'll have to take care that everyone gets a turn without the horses being ridden until they are exhausted.
Fun For Non-Riders
If there are non-riders, there are still fun things you can do. You can have showmanship, costume classes, and lead-line competitions that include games like turtle races and silly races that don't require too much riding skill but are still safe. One example of this is the carrot and cracker races.
For riders with minimum skills, someone leads the horse. (Good riders may ride by themselves.) All participants line up behind the start line. Another person waits at the other end of the arena with a few crackers and a carrot. The leaders take the horse and rider, or the horse is ridden to the waiting person. The rider then gets crackers and the horse gets the carrot. The rider (or the leader if the rider can't whistle) must eat the crackers and then whistle a short tune. When the tune has been whistled, and the horse has eaten all the carrot the team then races back to the finish line.
Where to Find Ideas
Check out outdoor games in books and websites for more inspiration for silly but safe races and games. Games like Simon Says, Musical Chairs, Mother May I, and Red Light, Green Light can easily be adapted for riding. Obstacle races can be set up over poles and around barrels.
Paint Your Pony
Another fun thing to do is 'decorate' the ponies. Using water-soluble, non-toxic bingo dabbers and water paints it's fun to use your pony as a canvas. Just be sure you have no shows scheduled right after just in case the paint lasts longer than expected. Most paints will wash right out. I've also known people to use the unsweetened drink mixes. These wash out quite nicely.
Games to Avoid
Anything that involves speed in a small space with lots of horses should be avoided. Even some traditional gymkhana games may not be suitable for small spaces like a small arena. Games that involve crawling along the ground, or using broomsticks or hockey sticks can be hazardous. Blindfolds and horses don't mix. Also, avoid anything that may spook horses.
Be sure that everyone follows guidelines for safety both on the horse and off it. Provide lots of awards-you can make certificates, create medals, or pick up little things at dollar stores. And have fun!