Recognize that he may just have a harmless crush on you, and doesn't seek anything more. If he tells you that you look nice in your dress or brings you an apple, smile and thank him. Understand that you may be his first role model, and that he looks up to you.
Talk to her in private if her behavior becomes inappropriate. If she starts asking you out on dates, let her know that she must stop her behavior immediately. For example, say, "Your behavior is completely inappropriate. Teachers can't have relationships with their students. I need you stop this behavior." Additionally, tell her that you will have to go to the principal if she doesn't change her behavior.
Schedule a meeting with the school principal if he continues to act inappropriately. Tell him one of your students is making advances toward you, and that you want it to stop. Give him examples of the times your student acted inappropriately, such as when he asked you out on a date.