While I’m training a youngster to first of accept a bit going in and out of its mouth, I want to use a Happy Mouth (by the way, these have been proven NOT safe to ride in), but because there is no joint and because they are plastic, they are perfect for babes to learn how to open their mouth to let the bit in and out without banging their teeth.
You could also use a rubber bit, but the plastic doesn’t chip off like the rubber can.
The first few times, I decide how to start. With some Babes, I put the headstall on with the Happy Mouth bit hanging on one side, and then slide the bit into the mouth and then slide it out. Each time with big rewards and praises. With some Babes, I put on the bridle like I would an experienced horse, first asking them to open their mouth and then slide the headstall over their ears. Again, always with many raises. It depends on the history of the youngster - if they had previously been a little bit touchy about the upper regions of their head, I prefer to place the headstall first and slide the bit in later. If they were easygoing about all things, then they get it put on normally. Play it by ear according to your Baby’s reaction and be willing to adjust accordingly. Eventually, all Babes learn to put it on like a normal horse, but it is a process. Most of them get the idea within a few tries. Most, if not all, enjoy all the fussing.
Once Babes is reliable about opening the mouth to accept the bit going in and out and has learned to keep its mouth open until the bit inches out (never drop it out) and happily stands while the bridle is put on and fussed over with the latches and whatnot, then I switch to a French snaffle. The French snaffle conforms to the shape of his mouth. I prefer full cheek pieces so there is no chance the bit can be pulled through his mouth while you are teaching Babes to follow and lead on the line.
Like mentioned above, I start with a halter under the bridle and lead them at first with that. Once they graduate to the idea of leading on the bridle, then remember that like riding, when leading in hand with a bit, always use a relaxed shoulder and elbow, and forgiving hand to follow movement, don’t allow your arm to do any tugging or resistance, which will actually teach resistance from Babes, always follow Babes’ movement. If they for whatever reason go backwards, you need to go with the flow to prevent pulling on their mouth which would complicate things and don’t drop the line! Have fun!