What is the theme in A Corner of the Universe by Ann M. Martin?

Coming of Age is the main theme. Hattie has a birthday in July. She ages physically from eleven to twelve. But Hattie also matures dramatically and notes that it can be at least partly attributed to Adam's presence in her life. Hattie doesn't know about Adam until shortly before his arrival, and she is filled with questions about him. Hattie encourages Adam to slip out of the house in order to go to the carnival and he does, but with disastrous consequences. Hattie is later talking to Nana, who says that Hattie should have known better.