the connection between ADHD and nutrition is brutally underrated, in terms of amounts per meal, intake of food additives and the mix as well. if starchy carbs, then very little fat and little protein. if meat, then no bread, no potatoes, no noodles or similar stuff at all. veggies are always fine except if the digestion of the kid says otherwise. sugar is a tricky thing. timing is important in terms of time of day and time after food intake but it works bad after some foods, which is different depending on geographical origin of grandparents.
you don't need to point a camera on the kid or anything. the effects of foods and the stuff that the body releases to digest the different compounds on body and brain become obvious within an hour or two. but you need to know the baseline(s) of your kid, e.g. time of day, after activities, around certain people, in places, crowds, moods, etc. make sure you do.