Is she allergic to the barley cereal?
I would defiantly mention it to your pediatrician. Celiac disease is an allergy to wheat, rye, barley, and oats, and parents often first notice it when a child starts on solid foods. Celiac disease is a fairly common condition. It effects about 1/100 people and requires an adherence to a strict gluten-free diet. Your doctor can rule it out with a simple blood test. The thing is that you have to actually be eating gluten on a regular basis for the test to be accurate, so talk to your pediatrician about your concerns BEFORE you change her diet. EDIT: Also while vomiting and rashes ARE a possible symptom of celiac disease, it’s much more likely that it would present with constipation or diarrhea, gassiness, and weight loss.
