Sat in a room with person A and B.
Person A and myself having a chat about our children and I told her a story of my son, when 4, once came to me with a box of tampons in the supermarket and said "do you need some more of these mummy" 
This is where person B who wasn't even involved in said conversation comes into the conversation by saying "what the F**, why would he know what tampons were at 4 years old" 
I explained that he had seen them at home, sometimes in my bedroom and sometimes in the bathroom.
She then went into a big rant about how she doesn't think it's suitable for children to see these things and there really is no need. I told her it's not something I have ever hidden in my house nor would I feel a reason to do so. I then left it at that, just a difference in opinion, surely?
Roughly 40 minutes later, person B suddenly says "ha I knew I was right!" I looked at her confused and she tells me that she asked on her group WhatsApp friends chat and they ALL agree with her about how it's wrong to have these on display to a child.
AIBU to be now really pissed off that she's made such a big deal over this -and would I be unreasonable to tell her to F off