A child taking the advice of trained and informed mental health professions that they are not ready to learn about something, say human sexuality, might preserve their emotional development.

Perhaps, but I'm skeptical that anyone's emotional development is really harmed by learning about human sexuality at an early age provided it's not done in a particularly shocking way. Sure, plenty of kids find it discomforting, and don't want to think about their parents "doing it," but does it cause lasting psychological harm? Without actual research backing up that conclusion, my initial guess would be "almost never."