Morally speaking, we are quick to plead innocence and absolve ourselves of responsibility solely on the basis of intention: It's enough for us that the soldiers did not intend to murder a mother and her two children at Qabatiyah, or that no one intended to kill five children in Khan Yunis. However, the absence of malicious intent is not a sufficient criterion. The fact that the Palestinian terrorists kill civilians with such intent while our soldiers refrain from killing civilians maliciously does not exempt the latter from responsibility. The question that has to be asked is whether the soldiers did enough to ensure that women and children would not be killed. Was the killing of Zakarana and her children unavoidable? Was it not the result of criminal negligence, even if not by intention?
The principle of collateral damage as justified and morally distinct from terrorism targeting civilians is one that demands serious consideration. It's worth noting essays like this one. The main point that I see here is that motive does not excuse killing - killing demands an investigation under law. If someone is killed and this is brushed away nonchalantly as "collateral" and no effort is made at an investigation and punishment for negligence then morally it IS the same as terrorism. To hide behind the shield of collateral damage you MUST be willing to take responsibility. That is the principle to which our own military does adhere, in afghanistan and also when we mistakenly bombed the Canadian troops. The difference in morality of the IDF and the American military is striking.