A child with celiac disease
who eats gluten
might have a large distended belly among other symptoms.
Strictly avoiding gluten would cure this symptom. However, there are other conditions that can cuase a large distended belly as well. It would be wise to have your child examined by a doctor.
For more on celiac see http://www.Celiac.Com/articles/1106/1/celiac-disease-symptoms/page1.Html.