I am so sorry about your loss! It is a huge tragedy for you and your family.
Just like you, I try to safeguard my child, and after a few years I have acquired a huge amount of skepticism towards nutritional science and research. So, I go with what my gut tells me: that fresh, non-processed food without added synthetic anything (be that oils, sugar, or preservatives) is the best; that time spent actively playing outdoors beats any other pass-time and that exposure to electronics should be limited to the minimum. I believe that non-glutenous real grains (not milled etc) and legumes can be added once in a while, but tubers are better. I do not cut milk, cheese and butter, but I would if I notice the signs of lactose intolerance.