The school should not take the parent out of the discussion related to any questions about sexuality. Children are already facing some changes with the hormones and changed to their body and encouragement from the school that their biological sex is not correct is wrong and not the responsibility of the school to discuss with the students.
Also the idea of allowing a boy into the changing room of the girls locker room is wrong.
Little girls using the same restroom of biological little boys is wrong and should not be an option in any situation.
Children could be going through questions about their body and it is not abuse for a parent to explain the differences without the fear of abuse charges from the school for not supporting children's sexuality questions.