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Not medical advice
While I cannot speak about kids, it is not infrequent to see adults who
have some type of break in the mucosal lining of the small intestine in
untreated CD.  Some of these breaks are actual ulcers some milder than
that.  I suspect that they are the result of the inflammation related to
the celiac disease.  Of course regular peptic ulcers are common at least
in the adult population. Usually in adults peptic ulcers are related to a
bug H. Pylori which if it is not present suggests that the ulcer is
related to celiac disease.
Joe Murray