Not all adults do what you suggest, by any means.
My parents are examples of that. I did not know until I was in my late teens that they were both atheists. They went out of their way to expose their three children to the beliefs of the dominant religion of this country. We were unceremoniously sent to Sunday School at a nearby Presbyterian church as children. Religion was otherwise not discussed at all. All three of us continued our church activities through high school, and our parents would show up if we were in some program at the church, just as they did for our school programs.
When I began having difficulties believing in the concept of supernatural entities in my late teens, I finally learned that my parents were atheists, and we discussed that at that time. My brother and sister are nominal Christians, but aren't active in organized religion.
My parents told me that they encouraged us to learn about the dominant religion so as not to unduly influence us. They had discussed it, and decided that we would be capable of making our own decisions at some point without their influence. It worked just fine.
Some parents do foist their beliefs off on their children. Not all, however, do that.
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