I'd recommend seeing if you have a teaching supply store in your local area. Ours, here in Indy, is United Arts and Education - it's phenomenal. http://www.unitednow.com/
As a Biologist, I'd really caution you to be careful even with simple chemistry because some household chemicals can not be mixed even though they seem benign.
"Sid the Science Kid" is phenomenal as well.
Simple things related to science:
1. Race cars teach simple physics
2. Gravity - why a wadded piece of paper falls differently than a flat one
3. Mentos + Diet Coke - that's a fun one
4. Mold - be careful unless you use pictures as many are toxic despite appearing safe
5. Leaves turning colors is science
6. Mushrooms sprouting is science (though, again, needs to be done really carefully as they're in the same genus as molds)
7. Mixing primary colors to come-up with secondary colors is science (my mom used to do it with food coloring and white frosting)
The list goes on and on and on and on. Rain is science. Clouds are science. Melting an ice-cube and refreezing it is science. My Molecular Biology professor used pipe cleaners to teach us the molecular structure of DNA - seems advanced, but our local living history museum had a display set-up on Sunday to do just that with a guide.
Growing plants is science - temperature, moisture, etc.
Good luck - sorry, you unleashed the nerd in me.