Let kids decorate homemade snow with syringes (you can get these free at pretty much any in-store pharmacy...just walk up and ask for them) and colored water. It's a hit every time!
To make the snow, just put ice and water in your blender. It takes a surprising amount of water to get the thick white slush...almost 50/50. Then fill short cups with water and food coloring...they'll do the rest! Be aware...they'll probably ask you to make them more than one bowl of snow :) The project can last longer if you crush more ice and fill a cake pan instead of just one small bowl. That also gives them more width to spread the colors over.
Enjoy and stay cool!
Love,
Family Support Center