The children will experiment, coming to the conclusion that air ever present. When air is cooled, it contracts and falls. When air is heated, it rises and expands. Air pushes on things whether it is moving or not. Air will take the shape of the container that it is in.
Air does have a mass.
The students will observe the results taking place. They will journal their results. This is one way. A candle cannot burn without the presence of air. You may want to work in groups of 2-4.