Zoe, you have been riveted by horses this year. When it was time to think about your birthday party, all you wanted was something horse-related.
Dad and I were not as sure about this. Horse back riding is expensive. It can be dangerous. The locations tend to be further away.
After talking it through with you, we made an agreement that I think reflects the kind of considerate problem solver you've become. We agreed to invite about half as many kids as you normally would, to make a cake and eat it at home (vs. rent a party room at the barn), make our own invitations, and you would make the goody bags yourself. You also researched horse-related charities in the mid-atlantic region and selected one with a good rating on Charity Navigator. You then made the invitations to include the charity information and suggested donations for the charity instead of gifts. For the goody bags, you wove a bookmark for each guest out of yarn in a colorful pattern.
We arrived at the barn and the kids were each paired with a helper and a horse.
From there, the kids were all fitted for helmets, and then brought all of their gear from the barn out to the stables themselves.
Each child groomed their horse with the proper combs for different parts of the body and used tools to get the crud out of their hooves. They also put on the bridles with some help and saddled up.

They had a series of balancing lessons and then played a game of putting rings over cones while on their horses, before taking a tiny trail ride and doing a little trotting.

After, they had a barn tour and ran through a relay race in the horse ring before setting out hay for the horses for the evening.
Back to our house for cake (cupcakes).
The day ended with a family dinner. Happy kids.
Blissfully exhausted Zoe.
Footnote: I know almost nothing about your class birthday celebration because in 4th grade parents aren't invited! I dropped off zucchini bread as a class treat (at your request), and you offered a water buffalo from Heifer as a class donation (thanks to another Milk Mom who taught us about Heifer). From all reports, you had a great day.