Used to hate it! Have to agree with everlong that if these people are your friends, then say something! I couldn't have survived without the mums that I knew and still know.
You've all got one purpose, to collect your child and take them home! I never got involved in playground/ school gate politics with people I didn't know, and really couldn't be bothered with it all.
If in doubt, put your big girl pants on, hold your head up high and stand on your own! As much as we all hate to admit it, we've probably been in a similar situation......and are still here to tell the tale
Good luck