Yes, ask questions. It sounds like you did fine. I think you'll find if you keep it up you'll actually develop a "patter," kind of a script, you know, of things to say. You'll figure out that *most* people understand when you word it a certain way. Think back to how your own trainer(s) taught you and take the best from their examples. Think about how you like to have things explained yourself.
"Do you understand?" is okay, but personally I prefer to ask, "Does that make sense?" Somehow it seems less condescending to me (but then I train adults, not kids). Another trick you can use is to ask them to explain it to YOU. And of course, have them do as much themselves as they possibly can (but help them out enough so they don't get frustrated).
If you keep giving lessons, you'll probably also realize that you need to teach things in a certain order (like tacking up before riding, LOL), and so you may be able to write out a "lesson plan" beforehand. Then you'll kind of have an outline in your head of what you need to touch on, and the words may come out easier.