My DS is only 2 so obviously isn't in school yet, but I have a 7 year old DSD who I pick up sometimes.
One mother there really has it in for me, always saying very loudly "that's just her STEPMUM." (Yep, lovey I am. Problem? You seem to love pointing that out. Although really I am not her stepmother I am daddy's partner, but go ahead and try and drill something in to me that I already know lol.) She glares at me every time I am there, and without fail will have sly digs about something or other. His ex thinks she is a loony too.
I never feel like I have a right to be there as she seems to think I am trying to play mummy when really, I am definitely 100% absolutely not.