oh boy my dd 4 (just about) is starting to go through this now and I'm freaking out because I was that girl at school with no friends. I just dropped her off at a birthday party and the host didn't even recognise her (her mother invited dd) it was a bit of a shock but dd didn't seem too concerned. I guess I'll talk to her about it later. Her kindy teachers say that she's happy alone but is getting to know some of the quieter kids and appears to be making friends. I'm quite scared because just like OP she has always been super social and confident - it just seems now that the developmental differences are getting too great for 4 year olds to be diplomatic about. I don't know many kids that age that like to be mother henned by a younger kid who can talk circles round them. argh. investigated one day gifted pre school for her for the social scene but worried that she won't be gifted "enough" to fit in there either...
