What an awesome opportunity to engage students in the User Experience! I love it when these things pop up naturally. If possible I'd have them brainstorm games that they like and how they conquer that issue. You could suggest (and an easy fix as well) that they place buttons on the screen that act like arrow keys, but what does that do to screen space? Could they figure out something else? What are they willing to give up for arrow keys, or could they reconfigure their game?
Interested to see how the conversation goes!