I have a sister a few years younger than I am who's been wearing a Hijab (her own choice) ever since she was little though I've noticed she's not as religiously inclined as she was when she was, say, 8 (young, I know.)
She did have a conversation with me about the origins of the universe and led the belief that it was created in 7 days, to which I immediately corrected her and calmly told her how the universe was actually created. I do regularly have quite casual conversations with her about religious morality and, as an older sister, encourage her to be kind and to not believe in such superstitious bullshit that Islam often spews out. I urge her to be open minded and to do as she pleases and stop assuming everything is a sin "because God said so". I also joke about hell so she can at least see it as laughable rather than fear it for the rest of her life. Luckily, it's much easier to explain things to someone younger. In my mind, it is possible to deprogram a child but it's important to remind them that they can believe whatever they want and encourage that
