I have twins and I know that at nursery , one of my daughters is playing with an older girl who has, in my opinion, taught her some bad habits. The other daughter plays with a completely different set of friends, in fact my two girls almost lead separate lives at nursery.
The one DD has started to tell me and her grandparents who care for her regularly to 'Shut up' and says 'You're stupid.' The other twin has never said this. I asked both girls where this type of language came from and they both said 'X' a girl at nursery who often speaks like that to the one daughter who plays with her.
I've spoken with my one daughter and she knows it's wrong but I'm a little disappointed that she's picking these things up at the age of 2.5 and that she's being spoken to in this way by another child.