We read Mouse Paint and did an expirement to see what would happen if we mixed primary play dough colors. The children loved being scientists. I used science resources by Denna Jump that can be purchased at http://www.teacherspayteachers.com/Store/Deanna-Jump-11
The Simple Science Volume 1 and Volume 2 and What Do Scientist Do? are excellent to teach small children about science and how to use the scientific method.