Well, I will say that I am a friend to my parents, but that only happened once I was older, got married, etc. Growing up, my parents were never my "friend." They mentored me, had expectations of me, and punished me when I was wrong. At the time I thought they were wrong, but hindsight is everything! In actuality, by sticking to their discipline, and making me to do so as well, they helped me grow into the happy person I am now.
Now that we are all grownups, though, my parents are my friends! We relate as adults, not with any family baggage, etc. My DH and I actually love to vacation with my folks, for example. We really all just get along and have fun. We are older than the kids I think some other posters have though (we're in our thirty mumbles, my folks in their late fifties).
My Mom jokes that I got all of my fighting out of me when I was a teenager. Well, I am glad we fought, and that she stuck to her guns when I was wrong or needed redirecting. So, be a parent now, and be a friend later, is my advice. It worked for us!