The Obama administration’s reaction came closest to the third response. It emphasized not that the school was endangered by Hamas but that the school was shelled:
The White House condemned the shelling Wednesday of a U.N. school in the Gaza Strip that was sheltering Palestinians displaced by the fighting between Israel and Hamas militants in Gaza. …
White House spokeswoman Bernadette Meehan also said the U.S. is “extremely concerned” that thousands of Palestinians aren’t safe in U.N.-designated shelters, despite being told by Israel’s military to leave their homes.
This is the height of irresponsibility. There is no principle of international law or convention that can enforce itself. When those principles are breached, it is some responsible party breaching them. The responsible party in breach here is Hamas.