So you want to introduce a bunch of young kids into the seedy underbelly of game development?
Honestly just let them get on with it and have a couple of playground punch ups over who gets what. If they loose a few dollers it may piss them off but they'll get over it. On the otherhand if you start drawing up contracts or getting legal guardians to take responsibility it could take one greedy parent to screw the whole thing up and end up in a legal wrangling that could put them off game development for life. At this age its supposed to be fun, let them think of making games as actually being a game and not some entreprenurial endevour.
If you are are teaching games development then teach games development. If you are asked about legal or entreprenurial stuff then just say "sorry I'm not a legal expert ask a law proffesor / lecturer or a Buisness studdies lecturer".
This is a good counter point on covering this material. However, my class goes into far more than just Design/GDDs. It also covers marketing plans, (as part of what I have them design to, is to figure out their market, and what would be sellable/of interest to their market.) it also talks about keeping a freelance team motivated/organized, etc... Its kind of an all encompassing attempt to give an introduction to all the different areas of developing a game that don't require specific programming or artistry skills. Of course it also focuses greatly on creativity and design.
Given that as the nature, I still plan on bringing this information up, though more as a 'think about this' type approach, rather than cover your a## requirements. I can agree about 1 greedy parent, or even a parent who sees their child as the brilliant leader and the rest of the kids as blundering idiots, and a feud starting between households. And then the Capulet family starts making accusations, and Mercutio steps in, but then he dies and all goes up in flames. Or is that some other story?...
Anyway, this gives me counter information to bring up, so its not so one sided as this is a good idea, blah blah blah. I'm not opposed to telling the students that one of their parents or them selves might become greedy, or severely misunderstand the work each person put into it, particularly if I approach it as a 'team-member's' parent, not as their own.. But perhaps even this is starting to establish distrust, between team members, and making them think too corporately to have fun.