I would be inclined to believe that it's still not causing the hyperactivity. Sugar is not a stimulant like caffeine,so any perceived effects are likely due to a child being told that sugar makes them energetic(placebo) or it may possibly be caused by the child simply being overly happy about getting sweets.
Now,there are certain chocolate bars that contain caffeine(if memory serves, it's added by the manufactures),but I dont know if cocoa or cacao plants themselves are caffeinated.
Theres also caffeine in some Soda/Fountain Drinks/Pop/whatever else soft drinks are called. So the energy parents see may be due to giving them drinks containing actual stimulants