I found this neat activity one one of my favorite kids' craft web sites, The Crafty Crow, http://belladia.typepad.com/crafty_crow/. It looked like so much fun, and included a bit of a science lesson. And being that the temps have been sub zero it was the perfect weather for building ice towers. The kids had a great time even if their finger did get a little frost bitten (just kidding). We filled the various containers with water, then colored them with food coloring. We were hoping to get some marbled blocks but the food coloring diffused through the water faster than it froze. We left the blocks outside overnight to freeze. It actually might have been a little too cold as we had cracks in a lost of our blocks. The ice blocks popped out of their containers quite easily and the kids got right to building. We used a sprinkle of salt to melt the surface of the blocks slightly. They would then freeze back together. Everyone had fun and voted to do it again. We are on the hunt for tall thin containers such as Popsicle containers.