In what places does Holden attempt to act like an adult? In what places does he enjoys being a child? How does each affect him emotionally?

Holden attempts to act like an adult when he visits the home of his aging professor, before he leaves Pencey Prep. He takes the advice given to him, however begrudgingly, but basically sits and listens politely. He does not put up much argument when he is told to make something of his life (I can't remember the professor's name, but it occurs in Chapter One.) He also attemps to act like an adult in a similar way when visiting Antolini, near the end of the novel. He listens, but his throbbing head and overall depressed attitude make it impossible for him to really focus on Antolini's words. To answer the other part of your question, one of Holden's most obvious demonstrations of immaturity, or "acting like a child" is during the scene with Sunny the prostitute. He is punched in the gut by her pimp, and suddenly he is pretending that he was shot, just for fun. Holden also enjoys visiting the museum of natural history, as it reminds him of his childhood (a place Holden longs to be but is cognizant at some level that he cannot go back, hence the depression.) What emotional impact do these places/scenes have on Holden? Like almost everything in the novel, the impact is that of depression. Holden is depressed at every turn. He can't go back and he can't go forward, and he knows it.