View attachment 36162
Kenosha News. 25 Nov 1999. Page 24.
Dude, you might want to read this article I posted earlier. It might provide the answer you are looking for regarding why charges were levied on minors for gun possession on cases from 20+ years ago, but not for the KR case in 2021. The other point is several of the articles you cited merely showed that charges were applied, or may be applied. It doesn't say whether the charges stuck or not. Perhaps they were dismissed, like the KR case.
EXPLAINER: Why did judge drop Rittenhouse gun charge?
Basically, the law has been updated multiple times in the last few years, for one thing. Another factor is the type of weapon and its barrel length can be the difference between legal and not.
It sounds like the law is somewhat obscure and a bit of a clusterfuck, and apparently its not often used. Perhaps the defense attorneys in the articles you cited were not aware of it. The attorneys in the KR case apparently discovered it and used it to the benefit of their client. Its their job. Its what they are hired for. I would hope that if you were a defense attorney, you would do the same for your client. Are these gun laws for minors appropriate? Arguably not, in which case perhaps an amendment to the law is appropriate. But until then, KR is a free man under the law.