These would involve your child eating a small amount of radiolabelled meal such as scrambled egg or drinking a small amount of radiolabelled fluid.  Then a special detector called a Gamma camera would be placed over the abdomen for periods every half an hour or hour for around 3 hours until the isotopic trace has left the stomach.  This is a non-invasive and accurate way to determine whether the stomach is emptying into the small bowel and the amount of Xray is minimal, similar to that which is encountered with standard x-ray procedures.