Wind is moving air. Air moves from places where there is more air pushing down (high pressure) to places where there is less air pushing down (low pressure). Wind can be gentle like a breeze or strong like a gust. We cannot see wind, but we can see and feel what it does -- it moves leaves, flags, clouds, and our hair.
Take children outside on a windy day and have them describe what they see moving. Use pinwheels, ribbons, or bubbles to make wind visible. Discuss the difference between a gentle breeze and strong wind. A simple fan demonstration shows that wind is just air being pushed from one place to another.
Air is all around you, even though you cannot see it. Most of the time you do not even notice it is there. But sometimes the air moves -- and when it does, we call it wind. Wind is nothing more than air in motion, flowing from one place to another.
Why does air move? Think about what happens when you open a bag of popcorn -- the smell spreads from where there is a lot of it to where there is none. Air works similarly. In some places, air presses down more heavily (scientists call this high pressure). In other places, air presses down less (low pressure). Air flows from the high-pressure place toward the low-pressure place, and that flowing air is what you feel as wind.
You cannot see wind because air is invisible. But you can see what wind does. It makes flags flutter, tree branches sway, and leaves tumble across the ground. It pushes clouds across the sky. It blows your hair and presses against your face when you ride a bike. All of these are clues that the air around you is moving.
Wind comes in different strengths. A breeze is gentle -- you feel it softly on your skin, and it barely moves the leaves. A gust is a sudden strong push of air. A gale is very strong wind that can bend trees and make it hard to walk. The stronger the wind, the more power it has to move things. That is why storms with strong winds can knock down branches or blow objects around.