I encountered two separate (and very different) sources commenting on the importance of who you hang around with.
This first quote gave me chills when I first read it:
How [your children] act around friends says more about the type of person they are turning into.
The second, related quote came from Tim Cook:
The [ethical] compass comes from parents and who you surround yourself with—friends. That collective group of people that influence you the most. [Developing your ethical compass] is largely the fact of others.