When preschool students are learning their colors, they are curious about mixing colors together and making different shades or new colors. Set up a station at your science table with paints, plenty of paper and some palettes. Choose the type of paint depending on your classroom style; if the children will be doing the activity all at once, provide tempera paints in paper cups. Otherwise, you may want to provide water colors or finger paints so they won't dry up. Allow children to experiment on their own or ask them to create or modify a specific color. Older students can make rainbows using prisms and then paint what they see.
Snag some helium balloons after a birthday party and let children watch how they float. Let them try to attach the balloons to small items to see how much a balloon can carry. Blow up some balloons with your breath and ask the children why those balloons do not float to the ceiling like the others. Have children record what happens to the helium balloons as days pass.
Set up a variety of different containers, such as plastic water bottles, Mason jars and baby food jars. Place some cups of water out and ask the children to pour some water into the containers. Demonstrate how to blow on the openings or tap the sides with a spoon to make a sound and have the children play with them. Ask why the containers make different sounds. Then students two of the same container and ask them to try to make the sounds match.
Springboard off of children's natural fascination with bugs and lay out materials to help students identify and study invertebrates. Provide field guides for your area and some bug flashcards or posters with pictures of bugs from other parts of the world. If you don't mind having them in the classroom, gather some grasshoppers, spiders or ladybugs in a bug catcher and keep them for a couple of days for children to observe at the science table. Talk about what bugs do, what they eat and how they grow.