On a day when it is actively snowing, grab some magnifying glasses, and dark paper or felt on your way outside. If nothing else, you can just use the children’s coat sleeves. The children catch the snowflakes and then look at them magnified.
Observe their different shapes, sizes, and symmetry. This is amazingly simple, but they get very excited. The wonder is that they are so perfectly shaped !!
Add a sensory experience by letting them catch the snowflakes on their tongues, or, if not too cold out, on bare skin, watching them melt.