We might be curious like in childhood, some child looks so ugly due to running nose carrying always a handkerchief but in adult looks so beautiful or handsome. So there is a gland known as adenoids present at the back of the nose. Its size varies in children from the size of walnuts up to Ping-Pong ball.
Furthermore, the nose normally produces as much as several liters of mucus/fluid to humidify and warm the air that is breathed, if the adenoids are large in case of some children, all that mucus backs up in the nose as it is not able to easily drain into the throat. This back up can result in symptoms of Rhinorrhea (runny nose). Luckily, the adenoids generally regress in size with age to the point they can be quite small in adults. Otherwise you can’t imagine a beautiful girl or boy in running nose mostly during their college time.