The time when it's difficult isn't when replying to emails which have been signed with a name (reply to full name, sign with full name - though someone will still get humphy about no title).
Its tricky when doing those annoying parent-child-teacher consultation days, when as a core subject secondary teacher you sit on a plastic chair for 10 straight hours, and parent plus child after parent plus child comes in to talk to you for 10 minute slots.
You have to establish what to call each adult. Obviously some aren't actually parents, so carer plus child (grandparent, sibling, dad's new girlfriend, foster carer ...)
I messed up the first year and made a performance of asking the child to introduce me from the second year, but of course they said "this is my mum/ sister/ Geraldine..." and I still didn't actually know how to address them. It takes up 1/10th of the time slot to establish introductions and dance about hoping they'll respond to your introducing yourself by actually telling you their name, and then you'll refer to them as Mr or Ms but they might be Dr or Professor or Rev, or want to be called Miss or Mrs...
Not to say it shouldn't be done, it should. Sometimes slipping up is excusable though!
I now realised we should have done a little lesson on formal introductions with every class - "Good afternoon, Ms Forests, this is my mum, Reverend Green, Mum, this is Ms Forests" ...
Bertrand I hope you aren't a pilot for a new initiative to triple the teaching retirement age?