Just a personal touch: my two daughters had food allergies (e.g. milk, soy). The second one had food allergies to almost everything in a way that you think you are cursed or crazy because there is a lack of research literature in this front. These were the kind of allergies related to immaturity and after the first year they were mostly solved. The "interesting" thing is that for the unsolved ones you can see behavior changes related to food.

If you are a parent it is important to write a personal ledger to keep the daily food interactions and think scientifically because medicine doesn't have solutions right now.