A few problems:
1. Hamas continued to celebrate the attack and call the criminals who carried it out "heroes" even after they knew they killed a kid
2. Hamas did not apologize for killing the kid
3. It was a big, bright yellow school bus, pretty hard to mistake for a green army vehicle
4. It wouldn't be the first time Hamas has celebrated killing children
Similar to when they were cheering and calling "heroes" the people who killed that pregnant mother.
1. Israel is continuing to kill children who get too near the 'exclusion' barrier
2. Israel did not apologize for killing any kids
3. They were kids in a farm field, hard to mistake kids in a farm field.
4. It wouldn't be the first time Israel has killed children.
The point is, by your own rationale, both crimes are an acceptable cost of 'war' (note that I disagree that the occupation can be called a war, its an occupation - see UN). None of your points call into dispute the lack of proof of intent to kill children.
In other words, your bias has blinded you to any clear moral system.
Killing children is wrong, why do you support Israel's killing of children?