Sink and float are one of the top science activities for preschool and kindergarten kids. I've seriously had 3 year olds stick with this for 50 minutes.
All tagged balloon
CD hovercrafts
A challenge to make a CD hovercraft results in engineering troubleshooting and a simple air pressure demo.
Catapults!
Building catapults takes nothing more than popsicle sticks and elastics and a bit of invention.
