A lot of good advice in this thread. While I can understand your hesitation about possibly restarting a bad dynamic with your family, the real question is "are they supportive now?" Because if they are, and if you think it would make you feel better to tell, then you should.
No, you don't blurt out with an I GOT MOLESTED. You set it up by saying you want to talk about something from the past that you're working on dealing with now, and/or confronting and explaining any characteristic acting-out or other aftereffects that they noticed at the time.
Getting the oldest secret off your chest can feel great. But it doesn't always end right there and you have to give them some time to process. I told my parents in December, and about a month ago my mom told me that "for many reasons" this had been the worst year of her life, and she started to cry. The ironic thing is that I was only really able to comfort her because of the huge step I'd taken for myself which had required kinda-sorta disregarding her feelings and bringing pain into her life.
Parenthood comes with pain, there is always the presumption of risk, it's why good parents always worry and fret. If it hadn't been CSA it could just as well have been a paralyzing car crash they'd have had to deal with - and they WOULD have dealt with it. They have no choice but to deal. Once you get that heartbeat, it is their job to deal. And it is unnatural for a child to take more pain onto themselves in order to deny the parent their rightful role of comforting and understanding their children.
Obviously the above only applies to good, involved, supportive parents. Any animal can squirt a baby out - parenting is about more than that, it's VERY much about giving your kids your all and taking the bad things with the good.
"Don't think it hasn't been a little slice of Heaven just because it hasn't!" --Bugs Bunny