DC's in reception and at the start of the year I noticed a number in the class WhatsApp group whose name I didn't recognise. I assumed it was possibly a grandparent of one of DC's classmates, Anyway, I also felt it was a bit busybody-like to look into it especially as I'm not even a class rep so left it. Fast forward five months and after I posted in the group offering some items for a school activity, the mysterious number messaged me asking if I could pass them one. I joked that I hadn't met them yet and they said that their child is in one of the other Reception classes. I'm not sure what to make of it as although our class WhatsApp isn't very active, some parents do post photos of their children after a party and to me it just feels weird (with privacy concerns) that this mum is still in a class WhatsApp group when her DC isn't in it. My question is: is it something I should mention to a class rep as she's been in the group for almost half a year already. WWYD? AIBU to mention it to a class rep?