Wow...fillyjonk...thank you so much for explaining that. I think you just helped me to understand my oldest daughter a lot better. She is very extroverted and I have always known that I need to be very careful with the people I let her hang around.
When she was younger we spent a lot of time together and she spent a lot of time with different adults(not without me, we just had a very social life, held lots of events, etc.). She had some play friends but not too many and they were always older than her. When we took a long trip and started taking her to parks all the time, she started developing some interesting characteristics, or at least they came to the fore-front. She would engage as many other kids on the playground as possible. Older kids, younger kids, she would sort of lead gangs of kids in games.
Around the time she turned 3 we met a friend for her who has a very manipulative personality. It definitely caused some strange issues. It caused an obsession with the color pink because the other girl would always fight about having the pink thing, and suddenly my daughter started doing that with her younger sister, or anyone, actually. That's just one example. A lot of the effect of that relationship is subtle and things that have taken me some time to understand. After that we had some neighbor friends she hung around all the time. It was very cliquey although there were only a handful of kids.
Since she's been 5, I've done some babysitting other kids and I definitely find that to be a strange experience. I usually will only have her around kids whose parents I vibe with, if she's going to be around them for a long period of time, but that hasn't quite been the case as of late. It seems to be okay because we have the ability to talk about how the other kids interact with her together. I don't babysit a lot, so she is still mostly engaged with me and her sister. I think this is really preferable at her age, because she kinda makes a big deal out of things and social interactions with other kids seem to mean a huge deal to her. I don't want her to experience any of those heartbreaking, manipulative moments before she has a chance to really establish more self-confidence and understanding of human behavior. I still want her to hang out with her friends, but when I do, I try to lead things in a way and have the kids with me most of the time. I think the regularity that builds in relationships is what allows "mob mentality" and similar adaptations.