How to deal with other parents at school

My kids go to a small school. I've been made aware of a group chat some of the parents have where they complain about teachers & other parents. They are all women in their 30s. They've discussed me and my child in their group chat. They're all nice to my face and have kids around the same age as my kid (5-6yrs) so I'm going to have to deal with them for the next 5 years atleast. I think it's pathetic and grown women shouldn't have a secret group chat to talk about people.They don't know that I know about their group chat. I have to see them all today when I pick up my 5 year old and I know they're all going to be fake as hell and act nice and friendly.I've never dealt with this sort of thing before, I have an older kid at the school but the parents for that age group aren't nasty and sneaky via /r/Parenting http://ift.tt/2gzReHz