"As atheists, we truly feel awful for you. And we promise to work for more gun control..."
First of all, that's a huge assumption. I would propose allowing concealed carry by responsible teachers and administrators.
But other than that, why would an atheist write this; to rub salt in the wound? Just because we cannot offer consolation doesn't mean we would go out of our way to upset them further. Why wouldn't a Christian write this if they were "being honest":
"Matthew 7:14 says that few will find the narrow road that leads to Heaven. Unfortunately that means that most of you will burn and never see your children again unless they, too, join you in the eternal fire."