Caffeine, sugar, and sodium! Most of these energy drinks are not even appropriate for adult consumption. Take Gatorade - it's fine - when you are working out, and working out enough to need it! But, there is no reason to drink it when you are not - no one needs additional electrolytes when they are sitting around the house. And children typically don't need these drinks at all.
Red Bull has 2-3x more caffeine than soda (which is another drink that is just awful for you from sugar to calcium depleting chemicals like phosphoric acid), has "mood stabilizers" don't really know what that means to out bodies, has quite a bit of sodium and too much sugar for one drink.
I say - stay away from it! Alternative - of course - water! But - kids don't drink that anymore - right? What about the iced teas that are natural - or something else that's natural. I only have a 2yr old - so I'm not there yet - but I drink water at home - if I'm out - I buy the Green Tea sweetened with honey (it's pretty natural overall). My husband drinks all those energy drinks - but they really are not good for you (I just can't quite wrestle them out of his hands!).