It seems you do not understand war crimes properly.
You can find out more here:
Israel is retaliating after the Hamas terrorist attacks with massive bombings, a total blockade of the Gaza Strip and possibly a ground offensive. What is covered by international law — and what constitutes a war crime?
www.dw.com
Obviously you didn't bother to read your own article so I will post the part that applied to this situation:
Self-defense — within limits
Israel's right to self-defense against armed attack according to Article 51 of the United Nations Charter is indisputable. This right, however, is restricted by international humanitarian law. Here, one of the most important principles is differentiation: The warring parties must differentiate between civilians and combatants, between civilian objects and military targets.
That only means, however, that civilians or civilian facilities are not allowed to be knowingly targeted in attacks. So, the killing of civilians is only forbidden when there is proof that it was done deliberately.
In practice, law professor Talmon explained, that means: "If Hamas positions a missile installation in a civilian neighborhood, Israel has the right to attack this missile installation — even at the expense of what is terribly called 'collateral damage' among the civilian population. And this collateral damage can, depending on the military goal and need, also be very high."
It is almost impossible to differentiate between civilian and military targets according to international law in the Gaza Strip, which has been under Israeli and Egyptian blockade since 2007 and is one of the most densely populated and built-up areas on Earth. Hamas tunnels run under apartment buildings; Hamas facilities are located in residential and office buildings. International law does not really account for this.
"If Hamas stays and hides in schools, mosques, hospitals, and operates command centers from there, then they become legitimate military targets," Stefan Talmon said. At the same time, it applies that: If Hamas sets up military positions in civilian areas, that counts as a war crime.