Similes are all about comparisons and they make writing interesting and create visual pictures to enable the reader to have a broader understanding of the meaning or significance of something. Similes use the words "like" or "as" in their descriptions, reinforcing similarities between between people, objects or abstract ideas, emphasizing things that may otherwise go unnoticed and sometimes creating similarities where otherwise there would not necessarily be an association.
In chapter 2 of The Boy in The Striped Pajamas, and having moved away from his beloved Berlin, Bruno is telling Maria (the maid) how much he dislikes the house in this "desolate" place which he mispronounces as "Out-With." When he sees someone come out of his parents' room, he realizes that it is not his father but another man who is not "as tall as" his father. He is comparing (who the reader will later discover is Lieutenant Kotler) with his father. The reader will soon realize that there are not many people who can be compared to Bruno's father.
A short time later, Bruno, the narrator, notices how Maria stands when a solider passes. She stands "like a person in prayer" and this emphasizes the feeling of fear that pervades the atmosphere when Bruno's father or any military personnel are present.
A less obvious simile is the comparison between the soldier whom Bruno and Maria have watched coming out of the room and a father. Bruno says that he does not think "that man looks like a father." It is usual to compare a man to being a father but Kotler will be proven to be particularly aggressive and harsh and this statement is preparing the reader by emphasizing Kotler's lack of human qualities.
Bruno is unable to explain his feelings about the house the family must now live in and so as not to "look like a baby," he tries very hard not to cry when he thinks about having no friends and only his sister Gretel for company. Bruno will later reveal a new level of maturity when he and Shmuel stand together in what is apparently the gas chamber and Bruno senses Shmuel's fear.