My daughter has celiac disease (more than a food allergy, a total intolerance to gluten, a protein found in grains like wheat, rye, barley, etc) Before we knew this, she was 2 and a half and had NO speech. After being correctly diagnosed (and by the way, lots of kids allergic to milk are also allergic to wheat) after two weeks in on a special diet, she started to babble, after about a month, she was putting words together, shortly thereafter, sentences. This was amazing, as she was previously in speech therapy for almost a year and we couldn’t get her to say anything. I believe the science behind it is that if you have a food allergy, it interferes with your ability to absorb nutrients and vitamins, and your brain becomes malnurshed and can not function properly. Do a search on “leaky gut” or “celiac” or “gfcf diet” (gluten free casien (milk protein) free diet and you will find a wealth of knowledge about food allergies, delays, etc.