A hernia is a sac of tissue which bulges out from the abdomen in the groin. Children are born with hernias, but may not have symptoms until they are older. Hernias occur more frequently in boys than in girls.
During fetal development, the testicles move downward toward the scrotum through a tunnel--the processus vaginalis. After the testicles are in place, the tunnel is supposed to close and disappear. Hernias form when the processus vaginalis does not close.
Girls may also have the tunnel and when it does not close an ovary, tubes, or intestines "pop out." In boys, it may be the intestines or testicle which "pop out."
Sometimes it is only fluid which "pops out" and then it is called a hydrocele--meaning "water sac." A hydrocele usually goes away by the time the child is 1 year old.