Here's an idea that could be fun :) as long as the horses have been desensitized appropriately for special occasions like Christmas and Easter or would be especially popular in the school holidays, you could do an 'own a pony day' they're quite common over here in England don't know about America where the kids get to come up in the morning brush and tack up their horses, with help obviously, and then what could be fun is take the kids to a local arena maybe do a quick lesson oorr work on a musical ride riding different figures and having to work in a team. Almost like a little dance routine on horseback xD then in the afternoon you could get like horse glitter gels (they do exist! haha) and ribbons and stuff and the kids could decorate their ponies and then could do a little performance for their parents I know if I was a kid I would love that! do you want me to see if I can find some musical ride videos to give you an idea of what I mean? :)
'Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming "Wow, what a ride!"'