My friend, Jolene, did a science experiment with our kids from this website.
http://pbskids.org/zoom/activities/sci/dancingraisins.html
The club soda is supposed to make the raisins dance. We also extended it to a sink/float activity where the kids made a prediction about whether or not various objects would sink or float. Then she had them glue the objects on a T-Chart with one side being for objects that sunk and one side being for objects that float. The kids had a good time and they REALLY enjoyed snacking on the raisins during the project.
To make this activity accessible to toddlers, for the chart, use pictures, not words, to show sink float. You can see that Jolene drew a picture with an arrow for the top of the jar and the bottom of the jar and she would say, "Do you think it's going to stay at the top or go to the bottom?"
To make this activity accessible to preschoolers, you can use a picture, along with writing the word so they are exposed to the print. I think we all like to expose our kids to print as young as possible, so you could do that with the toddlers, too, BUT, when they are preschool age, some of them can actually start copying the words, too.
