and I don't know how to fix it.
The kids and I literally stared at each other for ten minutes over this. I wanted to take them all outside and drown them in the pool. (I know it's not their fault, though, obviously.)
I don't have any other good way to come at this, though. Other options for asking relevant questions seem too ambiguous for this age group. Applications of triangle centroid are thin on the ground, or at least I haven't thought of any yet.