Science Discovery
Edmund Scientific has a thick catalog of really cool gadgets.
Magnetic Viewing Paper, available at edmund scientific $2
view magnetic fields. this is a really cool company for science gadgets of all types. many subjects.
Nebula Plasma Ball, available at edmund scientific $40
the famous glass ball that shoots electric plasma "lightning" to your fingertips. slight tingly feeling like when static raises the hair on your head.
MegaZooka (air vortex generator), available at edmund scientific $40
shoots a ball of air by creating a vortex. makes a fun toy, (though probably not for 3-year-olds). Read the description.
Radiometer, available at edmund scientific $12
heat from incandescent bulb or hand or sunlight causes the 4 vanes to rotate.
Equilateral Prism With Base, available at edmund scientific $13
set it on a windowsill, adjust, and look at the rainbow!
Diffraction Grating Glasses, available at edmund scientific $1
separates whatever you see into a spectrum of colors.
Solar Electricity Kit, available at edmund scientific $10
400x Illuminated Basic Student Microscope & Cordless, LED Model, available at edmund scientific $150
suggest you also get the beginner slidemaking kit $18 and a how-to microscope guide $6. they have more professional and also simpler/cheaper microsopes if you would like.