Even if they built these bomb shelters, Israel has bombs that could destroy them and I'm sure they would claiming there were weapon inside. When they are bombing hospitals, ambulances, and blowing up entire families, I have no doubt that they would bomb shelters as well.
Let's be real. If we were dealing with a Hamas who would use their resources to help out the community rather then endanger them there would be no bombings in Gaza. If Hamas spent the metal used to build rockets and instead built nothing but greenhouses Israel would have no reason to attack. But that is not what we have. We have a Hamas that hides 20 something missles in a school, hides things in hospitals and peoples houses. Then the world is surprised when Israel bombs those places after warning people to leave.