The three short stories, “The Cave”, “Two Kinds” and  “The Lie” are all about the pressures that kids go through to keep personal things in their life, but then  realize that they did not mean as much as they thought. 
In “The Cave” Charles met a bum who lived in a cave.  The boy was in a gang who was looking for a cave to make a meeting house in.  When the boy found a cave, he quickly told his gang. The gang then went to the sight of the cave, Charles was the first one in, he found that the cave was also the bums cave. The boy could not let the gang in, because the bum had been working on a bunch of statues in the wall of the cave. He was afraid that the boys would knock them down. So he told them that the cave was nothing. Then  the end of the school year begun and his parents made him stay in the house to study, he was not with the gang, so he did not know what they were up to, when school ended he went to visit the bum, but saw that the gang had found it and knocked over the bum’s statues, which drove him out of his cave.  
In “The Cave” Charles had to keep the bum a secret from everyone because if  the towns people found out, they would drive the bum out of the cave, and if the gang found out, they would also do something dumb, but Charles decision to not to tell anyone about it, led to the destruction of the bum’s statues.  In “Two Kinds” the girl’s mother told her she could be a prodigy.  But the girl chose not to listen.  She really could have been a prodigy, her decision not to listen to her mother changed her life forever.  In “The Lie” the kid probably would feel bad that he got his parents expectations up, and then told them about the school later when the damage was already done.