I believe all the decisions run in the *opposite* direction-- ie, people under 18 have no rights under the U.S. consitution because their parents are believed to be "acting in their best interests."
The parents have the right to sign them up for whatever school or religious program or behavioral program they choose-- regardless of the child's consent.
The U.S. did not sign the U.N. Convention on the Rights of the Child, which would have given youth some liberty rights. The only other country which refused to sign was Somalia.
American children are in the position of women before the vote and slaves before the civil war, basically.