Umbilical hernias most often close all by themselves--usually by the time a child is 4 or 5 years old. But some, especially children with very large umbilical hernias, require surgical repair.
When a hernia is very large, many surgeons will fix it when the child is 1 to 2 years old. Otherwise, waiting to see if the hernia closes on it's own is often the best course of action. If the hernia doesn't close as the child grows and develops stomach muscle, it will then be repaired with surgery.
Repair of the umbilical hernia is a surgical procedure. It requires an anesthetic agent, and your child will be taken to the operating room. It does not require a hospital stay unless your child has some additional condition that needs post-operative nursing care.