I think wheat, sugar, and all processed boxed foods should be the first to go. If you need to break that up in steps then that is o.k but all of those things need to go first. After you have removed those bad foods from the diet then I would work on cutting out other grains and also dairy that is not organic and full-fat.
At the same time that you are removing foods you can try to add some new foods that will take the place of the bad foods. My 3 year old daughter really loves eggs, kale chips, organic full-fat fermented dairy products, nuts/seeds, and most organic grassfed meats
Jaime, wife to Phaedrus and primal mama to A (4) and X (1).