Consider how much time you spend with your friends growing up. Peer pressure and influences from your friends are significant. In school you spend your days and free time with friends much more then with siblings and family. Your personal tastes and attitudes are shaped by this interaction much more than any other influence.
In the playground we play with anyone, and then we become more discriminating. Who we chose as friends in our youth will likely be there most of our lives. I still occasionally keep in touch with my first pre-school friend. Friends from high-school are still a significant part of my life. Do you have friends that you have known your whole life?
Keep your friends close, some day they may be the only ones who understand where you came from.