Only have a daughter, but we use correct terminology - vagina, vulva, labia, penis... I don't think testicles has come up. My daughter's only 16 months, but I try to use those in just the same way as I would with any other body part.
Eg. "I need to wipe your vulva now" (when changing nappy) or "yes, that's daddy's penis" (when pointing to her naked father and looking curious).
I feel like using nicknames for body parts keeps kids from understanding their own bodies well, purely for the comfort of adults.