It's always worth doing another demonstration or two - they also learn by watching what you do (assuming it's correct of course!).
Also landing is about attitude - if they roundout at the right sort of height and select the correct landing attitude,close the throttle (and whilst doing so still maintaining the correct attitude and keeping straight with rudder) they shouldn't go too far wrong. Remember also at this stage we are not aiming for precision but a safe technique. Have you shown them how to go around from a misjudged flare/landing? I think this is important because they need to know how to get out of trouble if it starts going wrong. Hope this helps.