Unless you sever all ties with family in my opinion they have a right to know, in addition to that I think it is pretty safe to say that once you get to a certain point you basically no longer want to hide.
When just starting out I advise to be very careful and be picky whom you tell. See how they react to the general subject before hand to help gage their expected reaction. That is generally a good way to go with anyone, parents included.
In my particular case my father asked me what was bothering me, I basically said that I was tired of being a boy. The conversation progressed from there. This worked for me in part because I am old enough and Mum and Dad know me well enough to trust my judgment; Our relationship is and has been very strong.
Who and how to tell people depend on a great number of things, what worked for me may not work for someone else;
I hope this is of some help to you.
