if its for a younger audience, what's going to be the challenge for them? is it luck dependent? preparation and calculation? or real time skill?
The only places where luck comes in are when the player enters a town/city/outpost the active "competitions" or "contests" for that town are generated, so there may only be 1 contest going at that time, or there could be 3-5 active contests that the player can choose to enter. Contests can be anything from an open field race against several animals, barrel race, sprint race, or some other type of obstacle race I haven't thought up yet.
The other place where luck comes in is when the player jumps over an obstacle/jump that has a "treat" floating above it. If they line up their trajectory to hit the treat it disappears, increments that treat count in their inventory and runs a stat gain function which may or may not award a stat gain for the animal which affects it's speed and agility.
The player has a taming skill and some animals have a minimum skill to tame, so they are locked until the player raises their skill high enough. I was also going to make certain animals spawn in certain areas like african animals spawn in the desert while farm animals are already on your starting farm and available from the start.
There's also a transition from trotting to gallop, once you go forward for 3 seconds the animation changes and your speed increases 50%. I could make stats reduce the time or maybe larger animals are slower to get up to max speed.
There are a couple games I'm drawing inspiration from, which are for a similar audience I'd like to target.
-"Spirit's herd", an old game where you play a horse as the main character looking for missing members of your herd.
It has some good non-combat ideas(buck off a rider in rodeo and escape, get water to put out fire, start an avalanche), and an open world. Throughout the world there are animals that offer you quests, ask you to race, or help you look for the missing animal/give a clue.
-"Barbie wild horse rescue" hehe I know it's corny and not something you or I would play, but it's similar with the riding around in my world looking for missing animals:
Then as far as making racing fun I'm looking at mario kart for ideas on power ups and course design, that game was fun for all ages.