Take a deep breath and have your class construct working models of a lung! Using 500ml plastic bottles as the chest cavity, and balloons for the lung and the diaphragm, learners work in groups to make a model. The models help them to visualize how the diaphragm works to drop the pressure in the chest cavity, allowing for air to rush into the lung. For younger children, you could make one as a demonstration during a human body unit or as part of the intended air unit. For older children, have them bring a plastic bottle to class and make their own.