Gastroesophageal reflux is when the stomach contents rise up into the esophagus and sometimes, babies spit up. I believe all newborn babies reflux to some degree, even if it's silently and you don't see it. This is because their lower esophageal sphincter, that's the muscle in the body into the stomach is not very competent in our youngest months of life. Reflux starts early on, as soon as right after birth, but it can begin around two to three months. It will generally last until nine months, when children crawl, they develop some skeletal musculature. That helps them to manage their spit up. Why do we care? We care because spit up can be more than just an inconvenience. Spit up can cause poor weight gain and it can be quite uncomfortable for the children. As that acid starts to rise up into the esophagus time and time again, it starts to erode the esophagus. The pain that they feel is perceived in their back and they'll do what's called the Standiford Sign, where they arch their back. What you see with children, which is distinct from colic, is that they are uncomfortable at all hours of the day, particularly after meals and they don't want to lay flat. If a child is not eating well, and not gaining weight, this should be managed. This is something that can be managed safely with antacids. Please discuss that with your pediatrician.