My mom and I were talking about this a few days ago.
My family isn't very 'religious', so to speak, but we consider ourselves Catholic. My mom was brought up to believe in God; she went to chuch every single Sunday, was baptized, read the Bible, etc. but now that she has my sister and I, she isn't strict at all concerning things like that. We still go to church a couple times a year, but basically only for holidays. She would not be disappointed, betrayed, or anything like that if we chose to follow a different religion, and the same goes with my father. IMO, a child should be allowed to follow whatever religion they choose, as long as they aren't hurting themselves, other people, or forcing their beliefs on other people like you said.

Since I don't plan to have any kids in my life, I don't think I can answer this.