Air gets cold in one place and hot in another place, air is made of atoms, and heat is made of energy, when atoms get cold they bunch together, because they don't have the energy to bounce eachother away, when air is hot, the atoms get farther apart because they do have the energy to bounce eachother away. Air doesn't like to be bunched up, so if it can go somewhere where it isn't so bunched, it will. When a bunch of cold, bunched up air meets a bunch of hot, unbunched air, air moves from the bunched in bunch to the unbunched bunch, and that movement of air is wind. Just omit the intro about heat and atoms and explain the bunches if he's too retarded.
