The notion of "minors' rights" is subject to case-by-case judicial review and is not universally acknowledged.
This link (
http://www.abanet.org/irr/hr/fall99h...ghts/budd.html ) discusses minors' rights in relation to curfews. The relevant passage is:
"...courts have excluded minors from the full reach of the Constitution and have held that the infringement of their rights is subject to less demanding scrutiny than the impairment of the rights of adults."
You'll find the same situation as regards "free speech and free expression" as regards minors. In comparison to adults, minors' "rights" are circumscribed.