Sometimes air pollution is very visible. Look out the window onto a busy street. Count the cars and trucks that pass by in a half-hour period. Note how many of them have visible smoke from their exhaust. All fossil fuel burners emit exhaust, but it is mostly unseen.
Shadows Go outside to a safe paved area.
Stand in a sunny spot. Have one person use chalk to trace the outline of another person's shoes and also their shadow. Put the name of the traced person in the outline of their shadow. Do this for each child. After an hour have each child stand in their shoes.