text: Dude.  Mentos and Diet Coke.  Sweet.  Someone's already mentioned it, but I will be a good scientist wannabe and provide a little more information here.\n\nI think diet has more oxygen than others.  You could test a couple of different sodas to see.  It's showing a physical reaction between the nucleation sites on the candy (imperfections, etc. that allow bubbles to form) and the gas in the soda.  The gas wants to form bubbles, and a nucleation site is where it can do so.  The candy sinks to the bottom of the soda bottle, making the reaction last awhile.  All those bubbles have nowhere to go but up.  \n\nYour experiment could be to see what soda does it the most, or what candy has the most nucleation sites (for six year olds, you could call them "bubble sites" or something).  Have them guess why the bubbles go up.  They might be able to figure out that it is because bubbles are made of gas and gas is lighter.  Hmm.  That brings us to solid, liquid, and gas; something they might have heard about in science class if they've been in first grade.\n\nYou'll want to try it at home first (but as a good camp counselor, you already know that).  \n\nAnother avenue you could explore is ecology.  Something like which food ants will eat first.  If you flood an ant hill (be careful they aren't the biting/stinging kind of ants), you can watch them evacuate their colony and carry their larvae away in a struggle for self-preservation.  That's kind of mean, though.  I bet they'd love to play with Mentos and Diet Coke.  I'm sure you could do a wonderful job explaining to them about bubbles and getting them to hypothesize about where the bubbles come from.\n\nGood luck!