I have taught many kids (and some of the best students were the very young boys!). The first thing you need to find out is how many are there to learn and how many are only there because their mom wanted them to be there - that will determine a lot about what you teach. I wouldn't spend very much time on machine maintenance. You can work that in as you progress. With kids I use the analogy of walking to school for the threading of the machine. Meaning that you always move forward, maybe taking a few side turns but continuing in a forward path.
Practicing on paper lines is a great thing to do. And when you have them pivot and turn corners until they have made a square, they really get happy. Pillowcases are good to get used to the machine, but the reason so many sewing classes start with pajama pants is that it is an opportunity to learn patterns, altering a pattern, layout, cutting sewing, and a waistband without too much concern over the fit and using cotton it is relatively cheap. I hope you have fun, I love working with kids and seeing how good they feel about themselves when they complete a project. Another word of caution. We tend to start sewing and forget time. Kids can only go about 2 hours without getting fuzzybrained.