Don't worry about it. When they are ready to receive that information, you will give. I never said directly to my parents that I am an atheist, but I declined to go to church, declined to pray, and never talked about religion as an adult.

I can still remember when I (with my two young daughters and wife)was visiting my parents one Christmas, my father said to me: "Do you want to go to church with me, son? I said no. He said, "I worry about your soul" I answered, "You worry about my soul. I worry about feeding my family.' The conversation ended. We never talked about religion again.