Let's cut to the chase: sugar doesn't make kids hyper. There have been at least twelve trials of various diets investigating different levels of sugar in children's diets. That's more studies than are often done on drugs. None of them detected any differences in behavior between children who had eaten sugar and those who hadn't. These studies included sugar from candy, chocolate, and natural sources. Some of them were short-term, and some of them were long term. Some of them focused on children with ADHD. Some of them even included only children who were considered "sensitive" to sugar. In all of them, children did not behave differently after eating something full of sugar or something sugar-free.
Even when science shows time and again that it's not so, we continue to persist in believing that sugar causes our kids to be hyperactive. That's likely because there's an association. Times when kids get a lot of sugar are often times when they are predisposed to be a little excited. Halloween. Birthday parties. Holidays. We may even be causing the problem ourselves. Some parents are so restrictive about sugar and candy that when their kids finally get it they’re quite excited. Even hyper.
I'm not sure I want to accept it, but there it is.