Children, especially when they are very young, don’t understand boundaries. They feel free to ask any and every question that comes to mind, and to give their opinion on whatever subject, regardless of who is involved. It is in the process of training a child that boundaries are taught. Thus, the child learns that it is not every question that should be asked, and that, unless you’re asked, you should generally keep your opinion about someone else’s business to yourself.
Apparently this only happens in ideal circumstances, and not everyone was trained or remembers what they were taught. How else do you explain the staggering number of adults who have no understanding of boundaries, and who cannot mind their business even if their lives depended on it?