I am fairly certain it is the food coloring that makes kids hyper (something usually paired with sugar in kid-favorite products). A common red food coloring agent is worst - the agents themselves have pharmokinetic effects. Not a big deal or anything, but something to keep in mind if you don't want the kids to be bouncing off the walls.
High fructose corn syrup...http://www.washingtonpost.com/ac2/wp-dyn/A8003-2003Mar10?language=printer
One of the kids in my class can NEVER have red koolaid or anything dyed red. it makes her so wild she can't sit still for a second.