Hello @logic42 :)
You have raised a very interesting point here: for a kid, witnessing someone living with dementia is very confusing indeed. Particularly in the cases when the person becomes sad and hostile. And you are right, it is heart-breaking thinking of such cases, even more so when they involve our loved ones. But, like you said, the prevention steps to be followed are SO simple that there is no excuse really for us to adopt and also for us to motivate the elderly members of our family to do the same!
Take Care my dear :)