Set up:
Make sure there's some space between kids, have them work in pairs.
Make sure there's warm water around (pitcher of water)
If you have a chance, put a spoon in the warm water while you take roll, etc.
Get attention of kids, give them rules, introduce yourself.
explain that we are going to play with something that most kids never get to touch. Drop dry ice (use spoon) in a glass of water, and sip it as it foams. Tell them that at the end they will get to try the same kind of drink for themselves. Pour some of the fog on a kid's head.
Mention that dry ice "sublimes" (turns into gas, not liquid) as it melts. Tell them you can demonstrate it (put warm spoon on a large chunk of dry ice. Press firmly. Let them hear it "sing."
Show how cold it is by putting water in teaspoon and count seconds until it freezes.
Give them water with a little bit of soap in it, let them play with the bubbles.
Make "fizzy drink"
Put the last of the dry ice in warm water, let them sit around fog, try to corral it. Talk about Halloween special effects.
Give teams a cup (or container) for water and straw
