I am incredibly shy in person as are most of my family members. The difference between being shy as a child and shy as an adult is that as an adult, people treat you very rudely. They are outright nasty to you and go out of their way not to include you in things. They will accuse you of being stuck up and of being "weird." It never occurs to most adults that shyness isn't usually a thing that you grow out of. No one would treat a shy child that way, but as an adult, it's a normal part of every day.