I was agnostic since the age of 12. At that point, I was still expected to attend church and didn't actually discuss it with my family until 10 years ago or so. That was about the time that I realized that I was an atheist. They are evangelical and I knew that it would be painful for them, so unless directly asked I skirted the subject.
I'm not going to get into what the "awakening" for me was on the board. It's so hard to explain without inadvertently stepping on someone else's toes, which I refuse to do. On another note, I will say that when we eat at my parents' house we always join hands and bow our heads with them when they pray (out of respect). When they came up for Thanksgiving and ate at my house, they didn't ask us to all join hands to pray. It was a beautiful, meaningful way for them to show that they respect my beliefs as I respect theirs. Of course they did bow their heads in quiet prayer and we waited quietly for them to finish before we ate. It doesn't mean that they are happy about it, but they have come to some kind of peace with it.