Colored "Glass" Fill small balloons with water & food coloring then pop the balloon once frozen. Then take them outside in the snow.
Subtraction War. I've done this and it's great!
Preschool Science Experiments: "Sparkly Explosion!" This website has lots of fun ideas to do with your preschoolers :)
balloon powered lego car...that looks really cool!...have a contest...see whose car goes the farthest!
Homemade pet jelly fish. that's about the neatest thing EVER. I did this with my 3rd, 4th and 5th grade class. Told them to bring in a bottle and a bag. Some of the kids brought it in and the rest of the kids thought it was dumb. After we did this project, the kids who thought it was dumb, didn't think so anymore. Kids who made them, named them and love them at home now.
jellyfish in a bottle!! craft for kids (...or your inner kid :) )