To give kids the most help, start them out using a rifle with an appropriate length of pull. All of these types of rifles are very good for training a beginner. Parents also need to be careful about observing all the rules of shooting safety. It is best to use very small loads in a muzzleloader, so the kid won't jump from recoil and the muzzle blast. Have kids wear ear protection at all times.
Eye protection is also essential.
If your young students can't hold up the rifle, have them shoot from a support such as cross sticks. Afterwards, he quizzed me by getting me a rifle, and I had to identify the important parts such as sights, safeties, hammers, triggers, the muzzle, and any other important parts of the rifle. The point is to get your student familiar with the rifle and its parts. During those times when Dad quizzed me, when I was doing my first shooting, we also shot various rifles that he had that were small enough for me to use. At that time we didn't have any benches to shoot from, so to make shooting much steadier for me, Dad would hold a pair of cross sticks while I shot at the targets.