More experienced people than I will probably chime in. I taught most of my foals to pony off of their dams, much like I taught them to get on a trailer with their moms. I’m just an ammy, but when I got around to backing my babies, having them ponied was a huge plus as they had company, my helper riding the lead horse had a lead shank on them so they couldn’t get their head down and buck (none ever tried FWIW), and I would gradually ride way from the lead horse. Very low stress
But assuming your foal is weaned, first lead the mare and the foal together. Then loop the foal’s lead shank over the mare’s neck, leading it from the side where it can’t follow just you (if your foal is likely to try to pull away, maybe loop that shank through a neck strap on the mare so the rope doesn’t end up under the mare’s tail). When that goes well, mount the mare and have someone lead the foal next to you as you walk around*. Still going well? Let them hand the lead to you. And off you go. Best of luck!
- I’ve had a couple of foals who were very comfortable with me on the ground become concerned when I was suddenly way taller and above them. But that’s why I started them loose with me on their dams. If mom says it’s ok, it must be ok!