Angelina I think it is at least illegal if it happens against the will of the child because children also have a right to develop freely sexually.
In Germany - yes. But would that hold true in very conservative states in the US? I am not sure your interpretation is a given there. You have to balance the right of a child to develop freely against the right of parents to decide how a child is raised. And in those very conservative states the second might well get the higher priority in courts.
But again, as long as this is not testet in court, we will never know and everything we say one way or the other is just speculation.