I got in on this discussion late, but I think the decision to continue the planned lesson is a good one. Acknowledging that some students may need help dealing with this very sad situation, that it is OK to need help, a moment of silence, time to talk, etc are all important.
It is one thing to respond artistically to something devastating (IE Katrina, 9/11) and a completely different thing to use art as a therapeutic tool.
Professional art therapists are trained to handle the emotions, conflict, personal situations, and concerns that arise and that may be opened up through the art where, as you noted, you are not.
You students will be helped by knowing that you care deeply and that you are there for them as you have been.