I was tickled as a child to be sure, but I certainly don't remember craving or even liking it then. I had no inkling of a tickling fetish of any sort until I came across some tickling sites on the internet while searching for foot stuff. Oddly enough, I quickly lost interest in feet, at least the level of interest that I started out with, and gained an interest in tickling just as quickly. It is very strange, because I can remember staring oddly at women's feet at a very early age and not understanding why, yet knowing I couldn't look away. These days I certainly don't mind looking at a pretty pair of feet, but there is no real drive or excitement associated with it like there once was. It is as if my foot fetish morphed into a tickling fetish, and considering how much fun I've had at gatherings and playing, I think it was a change for the better!
I think there has to be something in place there, even if it isn't obvious, right from the get go. When you say something like that, people always think, "Fetishes can't be genetic, that's just silly!", but I think there is definitely some sort of imprint in your mind from the earliest stages of development of how you will turn out. Environment and conditioning certainly play a role in many things and in many ways, but I don't think one should ever rule out "genetics" just because they don't like the implications.