This will amaze the kids. Your pal will be able to add, subtract or multiply. I like to have kids whisper in my ear how old they are and then have my donkey "guess" the right answer.
GloryB is going to show you how she counts. First, I stand near her shoulder, facing the same way that she is. My cue for her to count is I hold my hand on her shoulder while asking how old she is.
Sometimes it helps to put the toe of your shoe on the leg just above the hoof. As soon as she starts to lift her foot, I click and treat. It's not long before she will start "counting" with just my hand on her shoulder. My cue for her to stop counting is to take my hand away and step to the side just a little.
If you wanted, you could eventually move to the front of your guy and ask him how old he is. Your cue would be to point at his leg. Of course, the cue to stop counting would be to stop pointing.