So what exactly did the 8 year old boy sat in the back of his parents car do wrong?

I'll repeat the bit about professionals being trained to avoid and deescalate. That is the point. I think the details of this, and many similar incidents clearly show a lack of attempt to deescalate or avoid. That was the clear argument I made in my post and am re-emphasizing now. This clear trend shows either malicious intent by professionals or amateurs put in a situation they shouldn't have been allowed near and those above them should be held accountable for it.

Or in democratic societies we can insist that our "public servants" actually serve the public interest of law and order rather than merely using it as a pretext to be able to commit their own violent crimes.

Your rationalization is nothing more than a product of a failed society. Bringing it up as pragmatic advice might make sense, although still not for this incident where the "offense" seems to have been merely stopping a car on the side of the road. But invoking it as some universal value of "what ought" is a pure crab bucket mentality.

The IDF is not law enforcement. It's a foreign army. It treats Palestinians with utter contempt and has no problem with killing them. Its job is to protect Israeli settlers who are taking Palestinian land and to prevent the Palestinians from resisting Israeli rule.

Comparing the IDF to law enforcement in a democratic country is not relevant.