DIY easy bubble blower - made with empty water bottle! The kids loved it! There was a "fight" over a larger water bottle until the kids discovered you can make longer bubble "tails" with a smaller bottle (requires less air to blow).
Igloos are cool. What kid hasn't wanted to build an igloo? You can easily build an milk jug igloo in your classroom with some planning, lots of milk jugs and hot glue. This could be a fun winter craft for the kids when it's too cold to go out.
Make colored sand art by stirring a chalk stick in a bowl of salt. it changes the color. Stir less for light color and more for dark richer color. (I used to do this with salt and food coloring. but the chalk stick idea is brilliant!
Attention all my preschool teacher friends - Fish craft! Thanks to magnets hidden under the lid, this goldfish shimmies, quivers, and floats in its jam-jar bowl just like the real thing. way better then real fish!