I work with a PNP who has only worked with peds. So yes its possible to work only in peds and become a NP, especially if you want to be a PNP!
Good Luck!
PS And yes it is easier to handle some of the body fluids in peds. I used to work with in an adult ICU/PCU so I dealt with a lot of "big" people poop. I'd change a 3 month old's diaper any day compared to a 30 yr old.