I would suggest a simple pattern - 9 patch alternating with plain blocks - for them to start with. I would agree with the mentors doing the cutting for the entire group initially but then what about investing in some safety cutting gloves and letting at least the older ones cutting themselves. I would think if you kind of 'jumped in' to the quilt itself and teach the pressing and other intricacies along the way, it might hold the kid's interest a little more. If you hold their interest for a longer period, they are more apt to stay with it over a longer period of time. The LQS by me has summer 'quilt camps' for kids. They break it down into 2 groups by age - something like 7-12 yo in one camp and the 13-17 yo in another. Their attention spans are certainly different as well as comprehension levels.
Good luck with the project. Sounds like it could be lots of fun.