Childhood obesity, like all obesity, is most definitely about calories in vs calories out. However, it is also true that fructose (one half of sucrose), doesn't induce any of the body's satiety responses.

A second issue is salt, which induces thirst, which induced consumption of fluids. Solving that problem with water drops the osmolarity, which decreases the satiety signals by way of diluting the interstitium. Solving the thirst problem with beer, soda, milk, etc, maintains the osmolarity of the interstitium, but does so by way of increasing the blood glucose.

Overall, it's 90% eat less, 10% exercise more. But the exercise more is also critically important for increasing norepinephrine, which improves focus, willpower, concentration, whatever the amalgam of those words are that represents the effect of norepi.

Having seen really horrible outcomes in kids, please, please, give up this idea that calories in doesn't need to equal calories out. It does. Always.