First off I would suggest that you walk along holding the arm of whoever is riding. That way if something happens they don't fall clear off, this may make your son feel more comfortable as well. Also, depending on how big your mare is you might be able to stand over her back (like you are riding her, but not actually putting weight on her) and walk her around. Then slowly lower a little weight, not your whole body just enough she thinks a kid is on her. If she trys anything you can spin her in some circles or something as punishment. She should figure it out pretty quickly with something like that. Also, if that doesn't work and you really want her back for riding for your son you could desentise her like some people do with their big horses. I don't particularly reccomend it, but if you run out of options you can put yourself as well as your mare in a safe enviroment. Then use a soft cotton lead to make a rope with a loop (like a lariat the cowboys use) and place it around your mares middle. Lead her around and pull the rope tight around her girth, flanks, middle, any and everywhere between her front and back legs. In this way she will learn that when the kids grip with their legs it doesn't hurt her and that bucking has no effect on the "irritant" atop her. If your son isn't comfortable I wouldn't push the issue with him at least until you are sure the mare is not going to act up. Then be sure he knows you won't allow him to actually hit the dirt again. Best of luck
