Use chemistry to make a bouncing polymer ball, then alter the procedure to see the effect the changes have on the characteristics of the bouncing ball.: Make a Bouncing Polymer Ball - Introduction and Materials
The Stay-at-Home-Mom Survival Guide: Preschool Activities This is a GREAT site. Stay at home mom or go to school teacher!many clever and easy ways to work with your preschooler and have fun at the same time.
Naked egg experiment- Dissolve egg shell off with vinegar and it will become a "naked egg" that can bounce. A great experiment for spring break!- We did this and K loved it! I would suggest naked egg investigation be done outside.