Wow - I can't give you any real advice but you have my sympathy. I can understand why your dd may want to gravitate toward her age-mates but younger kids? Although even that is not a real problem. The big concern is that these kids are so mean to her. It isn't even all that subtle. Surely your dd can see through some of that? Any chance you can recruit her two real friends to help her see what's happening? If this continues, it may be advisable to get some professional input to avoid any real damage. You are right to be concerned.