Nowhere in Gray's Anatomy's 1,257 pages will be found a diagram of the tummy. Yet that's the nonspecific area where pediatricians are often told that it hurts. Tummy aches can range from GERD to food poisoning to allergies to a bacterial infection. There's even a chance it's a serious medical condition, as in this month's Puzzler, "Episodic pain in a school-aged child". Antacids, staying away from certain foods, and a few days of time will heal some of these ills. These links below describe numerous common GI conditions, in patient-friendly terms.
Abdominal Pain: http://www.chsd.org/body.cfm?id=605 An information page from the Rady Children's Hospital of San Diego.
Aerophagia: http://www2.kumc.edu/kupedigi/Aerophagia.htm An information page from the University of Kansas Medical Center.
Aphthous Stomatitis: http://www.childrensnyp.org/mschony/P01843.html An information page from the Children's Hospital of NewYork-Presbyterian.
Celiac Disease: http://www.celiac.org/ From the Celiac Disease Foundation.
Colic: http://www.healthsystem.virginia.edu/uvahealth/adult_pediatrics/colic.cfm/ An information age from the University of Virginia Health System.
Constipation: http://www.lpch.org/HealthLibrary/ParentCareTopics/AbdomenGISymptoms/Constipation.html An information page from the Lucile Packard Children's Hospital at Stanford.
Diarrhea: http://www.seattlechildrens.org/child_health_safety/health_advice/diarrhea.asp An information page from the Children's Hospital & Regional Medical Center of Seattle.
Encopresis: http://www.med.umich.edu/1libr/yourchild/encopre.htm An information page about soiling from the University of Michigan Health System.
Failure To Thrive: http://www.magicfoundation.org/www/docs/176/ An informational page from the Major Aspects of Growth InChildren (MAGIC) Foundation.
Gastroesophageal Reflux Disease (GERD): http://www.aboutgerd.org/ An information page from the International Foundation for Functional Gastrointestinal Disorders.
Giardia: http://www.cyh.com/HealthTopics/HealthTopicDetails.aspx?p=114&np=303&id=1947 An information page from the Children, Youth, and Women's Health Service of Australia.