In some treasure hunts, you only are given ONE clue, that leads you to the FIRST item - you have to find that to get the next clue. THAT item also has your next clue with it. That leads you to item 2, and so on. You have to find each clue, to get to the next item.
I've seen people use cookies, candy, apples, or horse treats for each clue.
And something nicer for the last thing you find.
So say, you have 4 people. And you decide to have 6 clues, and a final prize. Each person chips in a dollar for the prizes, or brings a prize or however you want to do that.
You would get 2 dozen little prizes - a cookie, an apple, something like that, enough for each person and each spot (4X6). Your final prize would be something nicer - say, a water bottle or a pair of grippy gloves or a lead shank.
SO. You decide on SIX spots to leave your clues. In a hole in a tree, on top of a barrel, on top of a fence, something riders can get to. You leave ONE clue, one LITTLE prize at each spot.
The first person who reaches the spot, gets the prize. He reads the clue and leaves it right there, and goes on to the next spot. And so on.
The clues are however hard your kids can handle. They could be pretty tricky for older kids. But you don't want to overdo as the youngest in the group needs a chance too.
So for example, everyone gets one clue - say, 'I am in the place where horses find shade' - and everyone rides toward a big tree. No clue there, humph! They ride to the lean to, and the first kid gets the carrot or cookie there - reads the clue and goes on to the next spot as fast as he can.
The others can read the clue he left, follow him and catch and pass him, if they think they understood the last clue, they might be going to the right place.
The idea is to get people to ride around a lot, mount and dismount, and have a lot of fun.