I guess the answer they are going for is slice the apples straight through, horizontally, 1/3 the way up from the bottom, so you have 2/3, 1/3, 2/3, and 1/3 apple portions. Then you give 1 person the 2 1/3 portions, and the other 2 get one of the 2/3 portions each.
But we all know the actual answer people are thinking of
You can cut them just like they are on the table - lop off the outer 1/3 of both the two as they sit. Two people each get 2/3 of an apple including the core, and one person gets two 1/3 apple slices.
But yes, it wants you to suggest killing one of the kids for sure. :)
Although I now see it too, I assure you with absolute sincerity that I really was trying to create an overhead view of two apples being sliced with one stroke.