Infants and young children often become infected with gastroenteritis leading to vomiting and diarrhea. This can lead to dehydration, one of the most common complaints in the Pediatric Emergency Department. These children are often in need of treatment with intravenous (IV) fluids. While the investigators know that IV fluids work, it is not clear which type or how much fluid is the best amount to give. Currently, the most common type of IV fluid given is salt water, also called normal saline.