Infant stomach, pediatrics, section of stomach wall. The infant's stomach is located under the liver. It is located more horizontally than that of the adult. So when the baby is lying down, the fundus is lower than the pylorus. The lower esophageal sphincter is immature, causing reflux. A child's digestive system becomes mature at 2 years old. Before he must eat more regularly and have more than 3 meals a day.