Gastritis and Ulcers
Many stomachaches in children result from gastritis (inflammation of the stomach lining) or an ulcer (an open sore or lesion on the stomach lining). The pain produced by either is sharp and concentrated between the bellybutton and rib cage; there's sometimes nausea and vomiting. Frequently these symptoms appear during or after eating -- especially if the food is acidic or spicy. (Orange juice or salsa-spiked tacos alone are rarely the cause of gastritis or ulcers, however.) For school-age children, an oral antacid like Mylanta can provide temporary relief, but if your child reaches the point where he's frequently asking for it, you should probably take a trip to the pediatrician.
Some ulcers and bouts of gastritis are associated with bacteria called Helicobacter pylori. Both are usually cured with a two-week course of a special combination of antibiotics, plus, for ulcers, antacid therapy.