On sunny days, the sky is clear and you can see the sun shining. On cloudy days, clouds cover the sky and block some or all of the sunlight. Some days are partly cloudy, with patches of blue sky between clouds. Clouds are not solid -- they are made of tiny water droplets floating in the air.
Have children look at the sky each day and classify it as sunny, partly cloudy, or cloudy. Use cotton balls on blue paper to model different amounts of cloud cover. Compare how the playground feels on sunny versus cloudy days to connect cloud cover with temperature.
Look up at the sky. If you see the bright sun and mostly blue sky, it is a sunny day. The sun sends light and warmth down to Earth, and on sunny days you can feel that warmth on your skin. If you step into the shade of a tree, you feel cooler -- not because the shade makes cold air, but because the tree blocks the sunlight from reaching you.
Now look up on a different day. If the sky is white or gray and you cannot see the sun, it is a cloudy day. Clouds are covering the sky like a big blanket. But here is something important: the sun did not go away. It is still there, right where it always is. The clouds are just blocking your view, like holding a sheet of paper between your eyes and a lamp. That is why cloudy days are still bright enough to see -- sunlight still gets through, just not as strongly.
Clouds might look solid, like big fluffy cotton balls, but they are not solid at all. They are made of tiny water droplets -- so tiny that millions of them float together in the air. If you have ever walked through fog, you have walked through a cloud. Fog is just a cloud that forms close to the ground instead of high in the sky.
Many days are partly cloudy, with some clouds drifting across a blue sky. You can watch the clouds move and see the sun appear and disappear as clouds pass in front of it. Paying attention to how much of the sky is covered by clouds is one of the first things weather watchers do every day.