"So now we're ceding defense of the Bill of Rights to the left?"\
Are minors entitled to the full scope of the BOR? I don't think so.
Your thinking on this is inverted. The Constitution is not a document which grants rights to citizens when they turn 18, or at any other time. It is a document that explicitly limits the actions taken by the government. There is no exception in the Constitution for the government's treatment of minors. If the kid's parents want to restrict his freedoms, search him unreasonably, etc., then they are fully within their rights to do so. The government is not.
Are minors entitled to the full scope of the BOR? I don't think so.
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The Bill of Right does NOT have a clause that says, "Except government school children and their parents!"