There are a number of methods that Holden uses to maintain a relationship with innocence and other methods he uses to resist advancement into adulthood.
Holden's relationship to his sister Phoebe and his continued relationship with his dead brother Allie both function as a means of preserving his own childhood and innocence. Holden identifies with his younger siblings and longs to keep the qualities he sees in them alive in himself.
We can see this clearly in Holden's dream of being a catcher in the rye and again in his experience at the park at the end of the novel.
The park evokes his own fond memories of childhood, before his brother Allie's death, and seeing Phoebe circling around in this natural setting seems to bring him a sense of permanency and wholeness.
Preserving ties to childhood is one of Holden's compulsions. It is matched by a twin compulsion to ward off progress into adulthood. We can see this in Holden's behavior at school, letting himself fail instead of working toward high school graduation. Another example of this tendency can be seen in the episode where Holden refuses to have sex with the prostitute.
Many of Holden's opinions also present his preference for innocence. The many things he refers to as "phoney" are often associated with adulthood, sophistication, and maturity.
Phoebe calls him out on this, saying:
"You don't like anything that's happening. . . . You don't like any schools. You don't like a million things. You don't."
The things that Holden likes, when he is pressed to name some, are emblems of his preference for innocence - Phoebe and Allie.