Since we've long since outgrown our sand and water table, I just filled a large plastic container with water and dumped in two containers of the water beads. The kids got the biggest kick out of the fact that the beads were completely invisible in the water and then magically appeared when you scooped up a handful. (I'll admit, I thought it was pretty cool too!)
As I mentioned, I used these clear water beads that I found in the dollar store. (They were in the floral section near the vases and floral foam). However, you can also find the dehydrated beads in tons of different colors at many craft stores ~ JoAnn's, Michaels, etc. ~ or online. You just have to put them in a container with some water and they will absorb the water and get much bigger.
This was a great lesson for me, but one that I should have known. So many activities that we think are geared to younger children, can be just as fun for the "big kids" as well. (and so many "big kid" activities can easily be adapted for the little ones with proper supervision.) I'm sure I'll be picking up more of these beads for the kids to play with over the summer.
For lots of great info on water beads from an amazing preschool teacher, check out Deborah's really informative post here at Teach Preschool ~ The Wonderful World of Water Beads.
And, for tons of great ways to play with your water beads, Melissa at the Chocolate Muffin Tree compiled this awesome list with dozens of fun ideas! ~ 32 Ways to Play with Water Beads