I used to think of myself as a Christian, back in primary school and the early part of secondary school. I was brought up in the Church of England. My first primary school was a C of E school, meaning that we had prayers in morning assembly and (one or twice a week) the vicar would come and tell us bible stories. For a while I went to Sunday school every week. I found this very boring and I'm sure I always used to say "It's Sunday - why do I have to go to school?".
In secondary school one day they handed out little red Gideon bibles to everyone in my year. I recall observing with horror when some of my classmates mutilated their copies. I read mine every day for probably the best part of a year. I don't recommend it - the writing style is really rather awful (I eventually gave up because it was so unreadable rather than through lack of faith).
Even amongst all this religious upbringing, I don't think I ever believed that the stories about Jesus and all the other bible stories were ever more than stories. They were just too ridiculous. In fact, I don't think it even occurred to me that there was anyone who ever thought of them as anything other than parables - certainly none of the religious people I knew ever gave me the impression they did. In fact it wasn't until I got to university that it sunk in that there were people who actually believed in the literal truth of the bible! This may seem strange to my American readers as this point of view is quite common here but I suspect it is the exception rather than the rule in England.
Even in the honors classes of every school, everywhere, (almost) everyone believes that whichever religion their family happens to believe is obviously the only possible truth, and that every other is obviously a ridiculous, meaningless pile of S. They've just learned not to say the last part out loud in public, to try to keep the hate and the murder rate down somewhat. If their family had happened to believe any other religion, they'd believe that that other religion, which they now believe is obviously ridiculous and meaningless, is obviously the only possible truth, and that the religion they now believe is obviously the only possible truth is obviously ridiculous and meaningless. They all just go along to get along, in a very weak and, above all, dishonest and cowardly, way, but, because almost everyone does that, it seems perfectly normal.