Not the parent, but I'll answer for myself: it's a good thing to have more people in your life in your formative years than just your immediate peers and your p

Not the parent, but I'll answer for myself: it's a good thing to have more people in your life in your formative years than just your immediate peers and your parents because you get experience developing more types of relationships with people. You understand how to relate to someone who is older and more experienced than you and has a different point of view than you do outside of the context of them having a direct authority over you. You also get exposed to more points of view than just your parents', which can be a good or bad thing depending on what those points of view are, but plurality on average tends to be beneficial, especially in your developmental years. By contrast, when you interact only with your self-selected peers of your own age group, your social circle becomes a bit of an echo chamber. In addition to the intellectual incest, if you don't have to deal with outsiders or people with different backgrounds or perspectives, you never figure out how to, and that's an important life skill. At the societal level, when people don't have to interact beyond their selected circle, they start becoming more insular, and that impedes the ability of groups to understand each other and communicate with each other, creating friction that can lead to conflicts and the inability to resolve such conflicts.