If the horse is younger, I would say that having an older horse would help, but it would be much better if it were someone that the baby already knew, not just a show up with another horse already in the trailer, and hope that baby hops in and takes confidence from a horse he's never met. As long as you don't make a big deal out of it, he shouldn't really have any problems. I had always been told over the years that in order to get a horse that loads well, you have to spend hours of time trailer training them, and working with them, so when I first worked my horse around a trailer, a week before I brought her home, I kind of expected fireworks or something, but she was actually pretty okay. On the day of the actual trailering, I stupidly lightly sedated her, as that was what the current trainer at that barn strongly recommended, and I really wish I hadn't. If she hadn't been sedated I think that she would have loaded just fine, but being sedated, she really couldn't think about anything that was going on, so she started getting a bit frustrated. She still loaded pretty easily, and once I got her home, she actually jumped back into the trailer when I was unloading her. She apparently didn't want to come out and meet the world. I also made sure that I has someone who was very experienced at hauling horses move her. A lot of the battle is the drive once you get the horse in. Try to make the trip as smooth as possible. Obviously some bumps, and stuff you can't avoid, but try to break very gradually as to not throw the horse against the sides of the trailer, take turns very slowly so the horse can adjust himself properly, as he doesn't have his "trailer legs" yet. And make sure you tell him he was a good boy when you get to where you are going.