There are a few conflicts going on in the book. I would say that the main conflict is the man vs. self conflict that surrounds Peter. Peter desperately wants to avoid growing up. To Peter, being an eternal child sounds great. He has few responsibilities outside of having fun. The conflict for Peter is what to do when Wendy invites him and the Lost Boys back home. On one hand, he wants to be around Wendy and the boys, but on the other hand he does not want to grow up. Leaving Never Land will guarantee that he grows up. In the end, Peter Pan chooses to stay forever young in Never Land. That sounds nice, but Peter is also forever alone.
Other conflicts in the story are between Peter and Hook and Hook and the Indians.