In our Magnets Bin, we have magnets of all shapes, sizes, and colors. These were purchased over the four years that I was a teacher (I had to buy them myself because in our county, Kindergarten doesn't cover Magnets, and I think that's just crazy. Kindergartners (and preschoolers and toddlers!) LOVE magnets. Capitalize on the natural interest, School Board!) But I digress. You can buy magnets anywhere, of course, but school supply stores usually have a great variety of shapes and sizes.
Here's some, ahem, "playing" happening:
Hmmm....they don't stick to this.....
This book is a great First Book about Magnets: