I honestly don't think getting off on the wrong side is a huge issue, in fact you should make sure your horse is OK with both sides because if someone happens to do something like that, you don't want them to panic on you.
I always mount from the wrong side, and I actually get off on the wrong side, its more comfortable for me, I didn't do it intentionally, thats the way our mounting block is set up. At first Lucky was dancing around unsure, but after a about three times he just quit caring. As for the walking off, thing, I definitely agree that is a bad habit.
I would get an instructor, kids seem to listen more aptly to someone that they don't know as well. With parents or family, they might do some eye rolling or a bit of sass. Which someone else, they may be more inclined to bit their lip and do as told.