That's WONDERFUL that you're going to do that. I have MD myself. When I was diagnosed with it the doctors told me parents to "take me home and make me as comfortable as they can for what little time I have left." Well, that was 25 years ago and here I am with a college degree!
Anyway, for me, it really frustrated me when people assumed I couldn't do things. But at the same time it also frustrated me when they assumed I could do things, and would stand there and watch me struggle. I'd say to let the kids try things on their own, and offer your help, until they (or a teacher, parents, etc) tells you different. Maybe you could ask the teachers of the kids ahead of time what specifically they need help with.
I'm so glad to read that you're doing this. When I was in school, other students were always willing to help me, but I hated always having to find someone and ask for help. Having someone just BE there to help would've been really nice.