Nope. I've never seen a true inguinal hernia disappear, but I have seen the bulge disappear in young children all the time. Since pediatric sacs usually have very tiny necks, they are often filled only with fluid which can move into and out of the peritoneal cavity easily. This is particularly true in infants, and often times you can't demonstrate the hernia when the parent brings the child in for consultation. But with a good history, the hernia sac is always there when you operate. I would therefore be suspicious that these children still have hernia sacs despite the negative exam.
Often the sac is filled only with fluid.