"Shakira Suglia, ScD, and colleagues from Columbia University’s Mailman School of Public Health, University of Vermont, and Harvard School of Public Health assessed approximately 3,000 5-year-old children enrolled in the Fragile Families and Child Wellbeing Study, a prospective birth cohort that follows mother-child pairs from 20 large U.S. cities. Mothers reported their child’s soft drink consumption and completed the Child Behavior Checklist based on their child’s behavior during the previous two months. The researchers found that 43% of the children consumed at least 1 serving of soft drinks per day, and 4% consumed 4 or more.
Aggression, withdrawal, and attention problems were associated with soda consumption. Even after adjusting for sociodemographic factors, maternal depression, intimate partner violence, and paternal incarceration, any soft drink consumption was associated with increased aggressive behavior. Children who drank 4 or more soft drinks per day were more than twice as likely to destroy things belonging to others, get into fights, and physically attack people. They also had increased attention problems and withdrawal behavior compared with those who did not consume soft drinks.
According to Dr. Suglia, “We found that the child’s aggressive behavior score increased with every increase in soft drinks servings per day.” Although this study cannot identify the exact nature of the association between soft drink consumption and problem behaviors, limiting or eliminating a child’s soft drink consumption may reduce behavioral problems."
“Soft Drinks Consumption Is Associated with Behavior Problems in 5-Year-Olds,” by Shakira F. Suglia, ScD, Sara Solnick, PhD, and David Hemenway, PhD, appears in The Journal of Pediatrics (www.jpeds.com), DOI 10.1016/j.jpeds.2013.06.023, published by Elsevier.
I found that news there: Soft Drinks and Behavioral Problems in Young Children
Well, if you imagine the large amount of sugar, and in some cases coffein, giving it to a five year old just doesn't seem to be a well idea. Their brains are still developing, and when getting so much sugar at that time already, they quickly adapt and get used to it. So naturally, it can lead to withdrawal symptoms, which again, can cause them to be more aggressive. Also, with soft drinks there can be quite some chemistry involved, and who knows what those do, maybe in the end it's not the sugar, but the other chemical additives in those beverages.
For example, certain artificial colors have been connected to stronger ADHD symptoms.
You can read about this here: http://www.webmd.com/add-adhd/childhood-adhd/food-dye-adhd
and here: http://www.rd.com/health/conditions/artificial-food-coloring-and-adhd-2/
But to give a bit "food for thought" (don't worry, no soft drink included), I will end here with a quote that I once came across when I had to write my first paper ever:
"For example, the desire for sweets can be instinctively a way out of emotional lonliness, lack of love, or intellectual overload. With the help of the sugar, the organism can create a temporarily strengthening of the self-confidence, but in the end, this only means a weakening, because it has been made without using the powers of ones own self. This weakening can show a strong desire for isolated sugars, even going into addiction, and the actual cause stays untouched. We can easily see, that in these cases we can only raise the misery with the "logical" explanations or even prohibitions."
A. Strauß; R. von Kries; B. Koletzko: Adipositasprävention im Kindes- und Jugendalter. In: Praxis der Naturwissenschaften vereinigt mit Biologie in der Schule. 11 (2005) 8 p. 23