I instruct a small group also but all of my students, from 2nd year student to black belts, take over the training of the class at some point. They learn from the experience and I get a better idea of how deep their knowledge is by how they instruct. 2nd yer people may only go through blocks or kicks with the class or the first form but I want them to be able to see mistakes and correct those mistakes.
Do I require them to do it, NO, they have the right to say NO, but they may not learn much more themselves unless they can give my a damn good reason for refusing to train someone else and pass on their knowledge.
As for them coming in when it is convenient for them, well , I kind of expect them to be in class because they are all students and are expected to know what is covered in class.
As for a ten year person, well I would like them to go out and start a school somewhere to help the system grow but if they work and live in town I can understand why they might want to stay at my school and help out .